Are you sending HTML or plain text messages?

Hi, the issue not about sending email, issue about new email text editing dialog. It simply add new signature and not remove previous, user still can manually remove not needed signature, but this isn't user friendly way, I think many people will miss this from time to time even if they know about this.

In your preferences, have you chosen to compose messages in HTML or Plain text?

HTML

changed to plain text, and issue still reproduce.

Please describe how to replicate the problem on https://demo.sogo.nu/ (sogo1/sogo1).

1. Login to https://demo.sogo.nu/SOGo
2. Go to Preferences -> Mail -> IMAP Accounts, link: https://demo.sogo.nu/SOGo/so/sogo1/Preferences#!/mailer
3. Edit sogo1@sogo-demo.inverse.ca
4. Add Signature to identity
5. This isn't work in demo but this optional: create new identity with signature
6. Save and go back to Mail link: https://demo.sogo.nu/SOGo/so/sogo1/Mail/view#!/Mail/0/inbox
7. Write a new message
8. Under Identity John Doe <sogo1@sogo-demo.inverse.ca> click on X and select again this identity. (If you have multiply identities you can switch between them)
9. Expected result: Signature for user John Doe <sogo1@sogo-demo.inverse.ca> will be removed from email body when you click on X and added new signature when you choose this\another identity
   Current result: No signature removed, new signature added. If you do step 8 multiply times - you will have multiply signatures in email body which need to be removed manually

Ho, but in demo it doesn't reproduce. Sec

I can reproduce it. The context of signature is important. Simple signature without HTML is work as expected, but signature as:
<b>Best Regards,</b><br>
Postmaster<br>
https://example.com/<br>
Phone: tel:+0000000<br>
will reproduce my flow