Email

Email signatures: what belongs in one, and what quietly bloats every reply

A signature is the most-seen piece of design your business owns, and in most companies it is also the reason a short conversation ends up weighing more than the document attached to it.

ByAlan Herbert11 August 20268 min read

Your email signature is almost certainly the most-viewed piece of design your business owns. It goes out dozens of times a day, it arrives in the middle of somebody’s working morning with their full attention on it, and unlike your website, nobody has to choose to visit it.

It is also, in most companies, the least considered. Signatures tend to be written once by whoever set up the email, copied by everyone who joined afterwards, and then left alone for years while job titles change and phone numbers stop working.

What a signature is actually for

It has three jobs, and they are smaller than most signatures assume. It should tell the reader who they are speaking to, give them another way to reach you if email is not right, and make it easy to find out more about the business if they want to.

That is genuinely all. Everything beyond those three things is competing with them for attention, and attention at the bottom of an email is in very short supply.

What belongs in one

Your name and your role, because the second one tells a new contact whether they are talking to the right person. The business name. A phone number that somebody actually answers. Your website address.

That is the core, and for a great many businesses it is the whole thing. If you have a genuine reason to add something, the usual candidates are an accreditation that matters in your trade, or a single link to whichever social account you actually keep up with. One that you post to is worth more than five that have been dormant since 2019.

What does not belong is easier to list, because it is the same handful of things every time. An inspirational quote. A legal disclaimer several paragraphs long, which is unenforceable and which nobody has read since email was invented. A request to consider the environment before printing, which by now costs more bandwidth than the paper it saves. A row of icons for accounts you do not use.

What UK companies are required to include

If you trade as a limited company, this part is not a matter of taste. Companies are required to disclose their company name, registered number, the part of the UK they are registered in, and the address of the registered office. That applies to business letters, order forms and websites, and business email is generally treated the same way.

It is worth checking your own signature against that list, because it is a common gap and an avoidable one. The usual way to handle it neatly is to put those details on their own line, smaller and quieter than the rest, at the very bottom. They are a legal requirement rather than something you are trying to draw the eye to.

If you are a sole trader rather than a limited company the requirements are different, so it is worth confirming what applies to you rather than copying a signature from somebody set up another way.

The image problem

Here is the one that causes real, measurable damage, and almost nobody notices it happening.

Most signatures include a logo. That logo is usually the file the designer supplied, which is to say a large one, several hundred kilobytes and sometimes several megabytes, intended for print. It gets embedded in the email, and it goes out attached to every single message.

Now think about what a conversation actually looks like. You email a client. They reply, quoting your message, which carries your logo. You reply to that, quoting their reply that quotes you, so now the thread contains it twice. By the twelfth message in a perfectly ordinary back and forth, that one image is in there a dozen times over, and a conversation containing nothing but a few hundred words of text is several megabytes in size.

This is not merely untidy. It fills mailboxes, which for most businesses have a hard limit that stops mail arriving when it is reached. It makes searching and archiving slower. And on a phone with a poor signal it means waiting for images to download before reading a one-line reply.

There are two other ways embedded images misbehave. Many email clients block images by default until the reader chooses to load them, so anything inside the picture is invisible on first read. And some clients strip the image out and re-attach it, which is where those mystery image001.png attachments come from, the ones that make a plain message look like it has a document with it.

Both of those lead to the same rule, which is the single most useful thing in this article. Your contact details must be live text, never inside an image. If your phone number only exists in a graphic, then for a meaningful proportion of your recipients it does not exist at all, and it cannot be copied, tapped, or searched for later.

If you want a logo, keep it small, a couple of hundred pixels wide and properly compressed, which should land it comfortably under 20KB. Better still, consider whether you need one at all. Your name and your business name in clean text is a perfectly respectable signature, and it survives every client, every device, and every setting.

Why replies deserve a shorter version

The full signature is useful the first time somebody hears from you. By the fourth message in a thread it is noise, and it is the mechanism by which the thread gets heavy.

Most email systems let you set a different signature for replies and forwards. A good reply signature is two lines: your name, and a phone number. Everything else has already been established. If your system does not support that, simply deleting the signature before sending a short reply takes a second and does the same job.

Keeping a team consistent

Signatures drift the moment more than one person is writing them. Somebody adds a title, somebody else changes the order, one person’s number has an area code and another’s does not, and within a year no two people in the business look like they work at the same place.

The fix is to write one, agree it, and apply it centrally rather than asking everyone to paste it in. Microsoft 365 can apply a signature across the organisation, which means a change of address or a new phone number is one edit rather than a chase around the office. It also means the legal details cannot quietly go missing when somebody sets up a new laptop.

Phones are the exception worth watching, because a signature set on the server does not always behave the same way on a mobile mail app. It is worth someone checking what actually goes out from a phone rather than assuming.

How to check your own

Send yourself an email from your normal setup, then reply to it twice so you can see what a thread does.

Read it on a phone. Turn image loading off and read it again, checking that everything important is still there. Look at the size of the message with a couple of replies in it. Try tapping the phone number to see whether it dials. Check that the website address goes where you expect, and that the details at the bottom still match reality, because registered office addresses and phone numbers change more often than signatures do.

If all of that behaves, you are ahead of most of the email arriving in your inbox this morning.

Where these facts come from

The disclosure requirements above are set out in law rather than in anybody’s guidance, so they are worth reading in the original if you want to be certain what applies to you.

Worth noting that the regulations name business letters, order forms and websites rather than email specifically. A business email is generally treated as a business letter in electronic form, which is why the same details belong in a signature, but that is the reasoning rather than a line you will find in the legislation.

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