Email subject lines that get opened
Builds guide sites for a livingPublished July 22, 2026Last updated July 26, 202613 min read
- A misleading subject heading on a commercial message is unlawful under a named federal provision.
- The standard is knowledge fairly implied on the basis of objective circumstances, so not thinking about it is no defence.
- A from line accurately identifying whoever sent the message is expressly not materially misleading.
- Any emoji forces an encoded form capped at 75 characters including charset, encoding and delimiters.
- Open rates now measure mail client behaviour, so judge subjects by replies, clicks and bookings.
A subject line is two things at once, and the advice sold about it treats it as neither. It is a legal statement about what the message contains, since federal law makes it unlawful to send a commercial message when you know, or reasonably ought to, that the subject heading would likely mislead a reasonable recipient about a material fact regarding the contents. And it is a technical field with published limits, one of which bites the moment you add an emoji. Between those two facts sit most of the tricks in circulation, and most of them do not survive. What is left is narrower, duller and considerably more effective, which is the usual shape of this subject. The rest of the client-facing writing sits under the getting-booked hub.
Four subject lines, and what each one promises
| Subject | Promise | Does the message keep it |
|---|---|---|
| Your Saturday, 6:23am | Details of their trip | Yes, if it opens with them |
| October dates are open | Availability | Yes, if dates are listed |
| Quick question | A question | Rarely |
| Re: your trip | A reply to something | No, unless it is one |
What does the law say about subject lines?
That a misleading one is unlawful, and it names the standard.
The provision is short and it is worth reading in the original rhythm rather than in summary.
It makes it unlawful to initiate the transmission of a commercial message where the sender has actual knowledge, or knowledge fairly implied on the basis of objective circumstances, that a subject heading would be likely to mislead a recipient, acting reasonably under the circumstances, about a material fact regarding the contents or subject matter of the message.
Three parts of that sentence carry the weight. Knowledge fairly implied, meaning you cannot avoid it by not thinking about it. A recipient acting reasonably, which is not the most credulous reader you can imagine. And a material fact about the contents, which is what the subject is describing.
Note what it does not say. Nothing about length, cleverness, capitals, questions or urgency.
The one thing it prohibits is a subject that misdescribes the message, which is precisely the thing most subject-line advice recommends.
This is general information rather than legal advice, and an operation with a real question about its sending should take proper advice on it.
The section is published at the Office of the Law Revision Counsel.
Does that outlaw the usual tricks?
It outlaws the ones that work by misdescription.
A subject reading like a reply, on a message that is not a reply, is describing the contents inaccurately in the most direct way available.
A subject implying a problem with a booking, on a message selling a trip, is doing the same thing more expensively, since the client opens it worried.
A subject promising a discount on a message with no discount in it fails on a material fact about the contents.
None of that depends on anybody complaining, and none of it is a matter of taste.
What survives is any subject that accurately says what is inside, which turns out to include every subject worth sending.
The commercial argument is the same as the legal one: a client who opens a misdescribed message learns that your subjects cannot be trusted, and the second one goes unopened.
The sender name side of this is covered in the piece on landing in spam.
What about the sender line?
The statute is unusually generous about it.
The same section states that a sender line accurately identifying any person who initiated the message shall not be considered materially false or materially misleading.
So sending as your own name rather than the business name is safe, and it is usually better, because a person's name in an inbox outperforms a brand nobody was expecting.
The provision that does bite covers header information obtained through false or fraudulent pretences, and header information that hides which machine sent the message, neither of which describes an honest operation.
What matters practically is consistency: pick one sender name and keep it, because the name is what a client's eye recognises before it reads anything.
Changing it between sends is the single easiest way to look unfamiliar.
If you send both personally and as the business, use the same form of your name in both.
Again, general information rather than advice on your particular sending.
What is the technical limit on a subject?
Not a character count, until you add an emoji.
The message format specification places two limits on any line in a message: each must be no more than 998 characters, and should be no more than 78.
It explains the harder limit as a matter of implementations that simply cannot handle more than 998 characters on a line, which is a practical constraint rather than a design preference.
Nothing there prevents a long subject, and the truncation people worry about is a mail client's display choice rather than a rule.
The interesting limit arrives with any character outside plain ASCII, meaning an emoji, an accent or a dash your word processor substituted.
Those cannot be carried directly, and must be wrapped in an encoded form defined by a separate specification.
That encoded form may not exceed 75 characters in total, including the character set name, the encoding name, the text and the delimiters.
The format rules are in RFC 5322, published by the IETF.
So what does an emoji actually cost?
Most of your usable subject, in the worst case.
Once the subject contains anything non-ASCII, the encoding wraps the text and the whole construction is capped at 75 characters.
Longer text has to be split across several such units, separated by a line break and a space, and any line containing one is limited to 76 characters.
The specification explains why the limits exist: to ease interoperability through gateways, and to limit how far a parser must look ahead before deciding what it is reading.
None of that breaks a modern mail client, and all of it means an emoji costs overhead in a field where overhead is invisible until something renders wrong.
Add the separate problem that a decorative character next to a name can read as an attempt to imply verification, which sending guidance addresses directly.
The honest conclusion is that an emoji buys attention from some readers and costs you nothing you can measure, so it is a taste decision rather than a technique.
Use one if it genuinely describes the message. Do not use one because a course said open rates rise.
The encoding is defined in RFC 2047, published by the RFC Editor.
What a subject line can carry. Take the eighty characters most desktop clients show and the roughly thirty a phone shows in a list, and write the subject so it survives the shorter one. That means the load-bearing words go first: the date, the water, the month, the thing that changed. A subject reading pleasantly for eleven words and only then arriving at the point is a subject nobody on a phone ever finished. Both display figures are approximations that vary by client, device and settings rather than published limits, and the only published numbers on this page are the 998 and 78 character line limits and the 75 character encoded-word cap.
What should a guide's subject actually say?
The most specific true thing about the message.
Almost every message a guide sends has one fact in it that the reader cares about, and that fact is the subject.
For a confirmation it is the date. For a week-before message it is the meeting time. For a cancellation it is the word cancelled and the date.
For a seasonal note it is the month and what is happening in it, which is more specific than the season and less specific than a forecast.
The test is whether somebody could reconstruct roughly what is inside from the subject alone, which is the same test the statute applies from the other direction.
Where a message genuinely has no single fact worth naming, the honest response is to question whether it needs sending.
That question kills more bad emails than any subject-line technique improves.
What belongs in those messages is set out in the welcome sequence piece.
Does personalisation in the subject help?
A name, no. A fact about them, yes.
A first name in a subject line reads as automated to almost everybody now, because it is, and because every business does it.
A detail only their message would carry reads as the opposite, and costs the same to insert.
The date they booked, the water they fished, the month they asked about: any of those is both personal and informative.
The distinction is that a name tells the reader you have a database, while a fact tells them you have their booking.
Where your tool cannot insert a real detail, leave the subject plain rather than falling back to the name.
A plain accurate subject outperforms a personalised vague one, and it is less work.
How to hold those details in a form you can actually insert is described in the segmenting piece.
What about questions, numbers and capitals?
Fine, unless they are doing work the message cannot back.
A question is a good subject when the message answers it and a poor one when the message ignores it.
A number is a good subject when the message is about that number, which for a guide usually means a date, a time or a count of open days.
Capitals do nothing except make a message look like the ones people delete without reading, and they are also easy to overdo without noticing.
The genuinely useful patterns are dull: a date, a place, a change, a deadline that actually exists.
What makes them work is not the pattern but that each is verifiable in the first line of the message.
A subject and an opening line that agree is worth more than any formula, and it is the thing nobody teaches.
Getting the message delivered at all is a separate matter, covered in the deliverability piece.
Should you test subject lines?
Only if your list is big enough to learn anything.
Split testing needs enough recipients in each half for a difference to mean something, and most guiding lists are well below that.
Running a test on two hundred people produces a result that will reverse next time, and acting on it is worse than not testing.
What does work at this scale is keeping a record: the subject, the date, the send size and what happened afterwards in bookings rather than opens.
Ten sends of honest record-keeping teaches an operation more about its own clients than any published benchmark.
It also survives the tooling changing, which a saved test result inside a platform does not.
And it points at the real question, which is whether the message produced a trip rather than whether it produced an open.
The seasonal send worth keeping records on is planned in the winter rebooking piece.
Why are open rates a poor target?
Because an open is not an event you can trust any more.
Opens are inferred from a loaded image, and mail clients increasingly load those images themselves regardless of whether a person read anything.
That makes an open rate a number describing your recipients' software rather than their interest.
The consequence for subject lines is direct: optimising a subject against a number that no longer measures attention is optimising against noise.
What still means something is a reply, a click to a page only that message pointed at, and a booking in the days after a send.
All three are countable without a platform, and all three are harder to fake.
The subject's job is to make an accurate promise, and the message's job is to keep it.
What to measure instead is covered in the piece on measuring without obsessing.
When should a subject line change between recipients?
Whenever the fact it names is different for them.
A single subject going to everybody is correct only when the message is the same for everybody, which is rarer than most sends assume.
Where you are writing to people who fished in different months, or booked different trips, the accurate subject differs and so should the send.
Splitting one message into three is a twenty-minute job and makes each subject specific rather than lowest common denominator.
It also reduces the number of people receiving something that does not apply to them, which is the quiet cause of most complaints.
The practical division for a guiding operation is usually past clients, people who enquired and never booked, and anybody who signed up on the site.
Those three groups want different things and will not tolerate each other's messages.
Where a tool makes splitting hard, send to the largest group and write to them rather than writing generically to all three.
What to send each group is planned in the gift certificate piece.
How do you write one when nothing has changed?
Find the thing that changed for the reader, not for you.
The hardest subject to write is the off-season message with no news, and it is hard because there genuinely is no fact in it.
The fix is not a cleverer subject, it is a better message: go and find something true about the water, the season or the calendar that the reader does not know.
A month opening, a fishery closing, a run arriving early, a gauge reading that changes what a trip looks like: any of these is a subject and a message at once.
Those facts are published and free, which means the constraint is attention rather than access.
Doing that once a season produces a message worth sending and a subject that writes itself.
The alternative, sending a message because it has been a while, is how a list learns to ignore you.
Where nothing has genuinely changed, send nothing, which is a decision rather than a failure.
Where those facts come from is described in the piece on building the list they go to.
Which habits waste a subject line?
Seven, and the first is describing a message you did not send.
Writing a subject that promises something the message does not contain, which is the one thing the statute names.
Dressing a send as a reply or a forward when it is neither.
Leading with the business name, which spends the first six words on information already visible in the sender line.
Front-loading pleasantries so the point arrives after a phone has stopped displaying the subject.
Inserting a first name and calling that personalisation.
Testing on a list too small to produce a result, then acting on it.
And judging any of it by opens, which now measure software behaviour as much as human behaviour.
Ideas for messages worth writing a subject for are collected in the newsletter ideas piece.
What surprises operators here?
That the subject line is regulated at all.
Most people assume the rules cover unsubscribes and addresses, and are startled that a specific provision addresses deceptive subject headings by name.
The second surprise is that the standard is knowledge fairly implied on the basis of objective circumstances, which does not reward not thinking about it.
The third is that using your own name in the sender line is expressly protected where it accurately identifies who sent the message.
The fourth is the 75-character cap that arrives with the first emoji, in a field most people assume is unlimited.
The fifth is that nothing in any of it says a subject must be short, clever or urgent.
What the rules actually require is accuracy, which is also what works.
The automated sends carrying these subjects are described in the automations piece.
The subject, in order
Say what is inside, shortest true version first.
Find the one fact in the message the reader cares about, and start the subject with it.
Check that somebody reading only the subject would correctly expect what the message contains.
Put the load-bearing words in the first few, so the subject survives a phone list view.
Use your own name in the sender line, spelled the same way every time.
Skip the first-name insertion unless you can insert a real detail instead.
Add an emoji only if it describes the message, remembering the encoded form is capped at 75 characters.
Keep a plain record of subject, date, send size and bookings afterwards, rather than testing on a list too small to learn from.
And never write a subject the first line of the message cannot immediately confirm.
No open rate appears anywhere on this page, for any subject line, any list or any season. That absence is the argument rather than a gap: opens are inferred from a loaded image, mail clients now load those images themselves, and a number produced that way describes software rather than readers. Publishing a benchmark against it would be dressing noise as evidence. The same goes for length, timing and word-count figures, none of which is asserted here. The published numbers on this page are three: the 998 and 78 character line limits and the 75 character encoded-word cap. Read 26 July 2026: the statute and both specifications. This is general information about a federal provision, not legal advice, and rules change.
How this was checked. The statutory material is quoted from 15 U.S.C. 7704, read at uscode.house.gov on 26 July 2026 in the preliminary edition. Subsection (a)(2), headed prohibition of deceptive subject headings, makes it unlawful for any person to initiate the transmission to a protected computer of a commercial electronic mail message if such person has actual knowledge, or knowledge fairly implied on the basis of objective circumstances, that a subject heading of the message would be likely to mislead a recipient, acting reasonably under the circumstances, about a material fact regarding the contents or subject matter of the message, consistent with the criteria used in enforcement of section 45 of that title. From subsection (a)(1): that header information technically accurate but including an originating address, domain name or internet protocol address obtained by means of false or fraudulent pretenses or representations shall be considered materially misleading; that a from line accurately identifying any person who initiated the message shall not be considered materially false or materially misleading; and that header information shall be considered materially misleading if it fails to identify accurately a protected computer used to initiate the message because the person initiating it knowingly uses another protected computer to relay or retransmit the message for purposes of disguising its origin. The line limits are quoted from RFC 5322, Internet Message Format, read at datatracker.ietf.org the same day, section 2.1.1: that each line of characters must be no more than 998 characters and should be no more than 78 characters excluding the carriage return and line feed, and that the 998 character limit is due to limitations in many implementations that send, receive or store messages and simply cannot handle more than 998 characters on a line. The encoding limits are quoted from RFC 2047, Message Header Extensions for Non-ASCII Text, read at rfc-editor.org the same day: that an encoded word may not be more than 75 characters long including the charset, the encoding, the encoded text and the delimiters; that where more text is needed, multiple encoded words separated by a line break and a space may be used; that while there is no limit to the length of a multiple-line header field, each line containing one or more encoded words is limited to 76 characters; and that the length restrictions exist both to ease interoperability through internetwork mail gateways and to impose a limit on the amount of lookahead a header parser must employ before deciding whether a token is an encoded word. The display figures in the arithmetic panel are described there as approximations rather than published limits. No open rate, click rate or subject-line performance figure is asserted anywhere on this page. General information, not legal advice.
If your booking calendar has more open weeks than you’d like, I’ll build you a free preview of your booking site before you pay a cent.
Get a free website previewSubject lines that get opened, the questions that matter first
Is there actually a law about subject lines?
Yes, and it is specific. 15 U.S.C. 7704(a)(2), headed prohibition of deceptive subject headings, makes it unlawful to initiate the transmission of a commercial electronic mail message where the sender has actual knowledge, or knowledge fairly implied on the basis of objective circumstances, that a subject heading would be likely to mislead a recipient, acting reasonably under the circumstances, about a material fact regarding the contents or subject matter of the message. Three parts carry weight: knowledge fairly implied, so not thinking about it is no defence; a recipient acting reasonably; and a material fact about the contents. This is general information, not legal advice.
Does that rule out the usual tricks?
It rules out the ones that work by misdescription. A subject reading like a reply on a message that is not a reply misdescribes the contents in the most direct way available. A subject implying a problem with a booking, on a message selling a trip, does the same thing more expensively, because the client opens it worried. A subject promising a discount that is not inside fails on a material fact. Notice what the provision does not mention: length, cleverness, capitals, questions, urgency. The commercial argument matches the legal one, since a client who opens a misdescribed message learns your subjects cannot be trusted.
Can I send under my own name?
Yes, and the statute is unusually explicit. It states that a from line accurately identifying any person who initiated the message shall not be considered materially false or materially misleading. Sending as your own name rather than the business name is therefore safe, and it usually performs better, because a person's name in an inbox outperforms a brand nobody was expecting. The provisions that do bite cover header information obtained through false or fraudulent pretenses, and header information that disguises which machine sent the message. Practically, pick one sender name and keep it, since the name is what a client's eye recognises first.
How long can a subject line be?
Longer than you would ever want, until you add an emoji. RFC 5322 places two limits on any line in a message: no more than 998 characters, and no more than 78 by preference, with the harder limit explained as a matter of implementations that simply cannot handle more. Nothing prevents a long subject, and the truncation people worry about is a mail client's display choice rather than a rule. The real constraint arrives with any non-ASCII character, which must be wrapped in an encoded form defined by RFC 2047 and capped at 75 characters including the charset name, encoding name, text and delimiters.
What should a guide's subject line actually say?
The most specific true thing about the message. Almost every message a guide sends has one fact the reader cares about, and that fact is the subject. For a confirmation it is the date. For a week-before message it is the meeting time. For a cancellation it is the word cancelled and the date. For a seasonal note it is the month and what is happening in it. The test is whether somebody could reconstruct roughly what is inside from the subject alone, which is the same test the statute applies from the other direction. Where a message has no single fact worth naming, question whether it needs sending.
Does personalisation help?
A name, no. A fact about them, yes. A first name in a subject reads as automated to almost everybody now, because it is, and because every business does it. A detail only their message would carry reads as the opposite and costs the same to insert: the date they booked, the water they fished, the month they asked about. The distinction is that a name tells the reader you have a database, while a fact tells them you have their booking. Where your tool cannot insert a real detail, leave the subject plain rather than falling back to the name, since a plain accurate subject beats a personalised vague one.
Should I optimise for open rates?
No, because an open is no longer an event you can trust. Opens are inferred from a loaded image, and mail clients increasingly load those images themselves regardless of whether anybody read anything, which makes an open rate a number describing your recipients' software rather than their interest. Optimising a subject against that is optimising against noise. What still means something is a reply, a click to a page only that message pointed at, and a booking in the days after a send. All three are countable without a platform, and all three are harder to fake.
Sources & methods
- 15 U.S.C. 7704, Office of the Law Revision Counsel
- RFC 5322, Internet Message Format (IETF Datatracker)
- RFC 2047, MIME Part Three: Message Header Extensions for Non-ASCII Text (RFC Editor)
Every figure here is traced to a named public source and checked against it. Licensing, tax, and fee rules change. Verify your state’s current rules with the agency directly before you count on any number here.
Evan Knox
I build booking websites and run the ads and search for owner-run fishing guides, one operation per stretch of water. My first guide client, Bowman Fly Fishing, grew its revenue 4x in a year from that work. Field Notes is where I put the straight numbers on the business of guiding.
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I'm Evan, and the guide whose emails say exactly what they contain, and point at a site that books cleanly, is the one who fills a calendar. I build booking sites and run the search and local SEO for owner-run guide operations, one operation per stretch of water. Text me at (470) 777-9686 and I'll build you a free preview of your site before you pay a thing.