The most common cause is that you are using the new Outlook while the signature was set up in a way that only applies to classic Outlook. Other frequent causes are a signature set for new messages but not for replies, an add-in that was never assigned to the user, and images the recipient's client blocks. The causes below are ordered by how often they are to blame, each with a check.
First: which Outlook are you using?
This matters most, because classic and new Outlook keep signatures in different places. The new Outlook has a New Outlook toggle at the top right and looks like Outlook on the web. Classic Outlook has a ribbon with File, Home and Send / Receive tabs.
| Classic Outlook | New Outlook and web | |
|---|---|---|
| Where the signature lives | Files in the user profile, and in recent versions also the mailbox | In the cloud mailbox |
| Scripts that write signature files | Work | No effect |
| COM add-ins | Work | Not supported |
| Web add-ins | Work | Work |
If the signature was set by a logon script or Group Policy, it will never appear in the new Outlook. See Signatures in the new Outlook for Windows.
Ten causes, in order
1. The signature is set for new messages but not for replies
These are two separate settings, and replies often default to none. Check File → Options → Mail → Signatures (classic) or Settings → Account → Signatures (new): are both the new-message and the reply box set?
2. The add-in is not assigned, or does not start
If a web add-in inserts the signature, an admin has to assign it to the user in the Microsoft 365 admin center (Integrated apps), and it takes time to roll out. Check Home → Get Add-ins → My add-ins to see whether it is listed, then restart Outlook.
3. The signature is in the mailbox but has not synced yet
Signatures stored in the mailbox reach the client with a delay, sometimes ten minutes or more. If you just changed the template, wait before hunting for a fault. A quick check: open Outlook on the web — if the signature is there, the setup is right and it is only sync.
4. A transport rule is invisible to the sender
If a rule in Exchange Online adds the signature or footer, you don't see it while writing. It is added once the message leaves the server. That is not a fault. Check by sending to another address of yours and looking at the received copy, not the sent one.
5. The recipient's client blocks images
The logo is often missing only for the recipient, not for you. Many clients don't load external images by default. The image has to sit on a publicly reachable address rather than an internal server, and needs alt text so the message still reads without it.
6. The message is in plain text
Plain text carries no formatting, colours or images, so the signature appears as a bare line or not at all. Check the message format on the Format Text tab and switch it to HTML.
7. The phone has its own signature
The Outlook app on phones has a separate setting, often defaulting to "Sent from Outlook for iOS". The desktop setting does not affect it unless an add-in inserts the signature or it is stored in the mailbox. See Signatures in Outlook on the phone.
8. Several accounts or profiles
A signature belongs to an account. If Outlook holds more than one mailbox, make sure the signature is set for the one you are writing from, and that the right account is selected in the signature window.
9. A cloud signature overrides the local one
Recent Outlook versions store signatures in the mailbox rather than in files. If a tool or script wrote files, the local signature disappears once the client switches to mailbox-stored signatures. The fix is not to go back to files, but to use a tool that sets the signature in the mailbox or inserts it with an add-in.
10. Someone deleted it from the draft
It sounds trivial but it happens constantly: replying and deleting everything below your own text removes the signature too. In long threads it goes together with the quoted text.
How to fix this once, for everyone
Most of the causes above come from each employee setting up their own signature on their own computer. A central tool removes that: one template, details from the directory, delivered through an add-in or the mailbox, so it is the same in classic and new Outlook, on the web and on phones. A comparison of tools is in Best email signature software for Microsoft 365.
Frequently asked questions
Why is my email signature not showing in Outlook?
Most often because you are using the new Outlook while the signature was set up in a way that only applies to classic Outlook, such as a script that writes signature files. Other common causes are a signature set only for new messages and not replies, an add-in that was never assigned to the user, and images blocked by the recipient.
Why is the signature missing in replies but present in new messages?
They are separate settings. Next to the new-message box in the signature window there is a box for replies and forwards, and it is often set to "none".
Why can't the recipient see the logo in my signature?
Because their client did not load the image. It has to be on a publicly reachable address rather than an internal server, and it needs alt text. Some recipients never load images, so the signature should work without them.
Why can't I see my own signature while the recipient can?
Because a transport rule adds it as the message leaves your mailbox, so it is not there while you write. That is expected behaviour for Exchange Online rules, not a fault.
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