I'm using Roundcube mail client

Here is a short description of how you can add a signature in your emails in Roundcube mail client.

Note that this signature applies only to mail sent with Roundcube. Signatures for emails sent by third-party clients need to be configured in that particular client.

1. Login to your mail account with current credentials using Roundcube: mail.svenskadomaner.se.
2. Click on Settings in the upper right corner. (1)
3. Click on "Preferences" in the left panel. (2)
4. Click on "Composing messages" in the second panel. (3)
5. Change the "Compose HTML messages" to "Always" in Main Options section.
6. Make sure that "Automatically add signature" is set to "always" in Signature Options section. (4)
7. Click on the "Save" button. (5)
   
8. Click on "Identities" in the left panel. (2)
9. Select the email account that you want to add the signature. (3)
10. Enter your desired signature.
    If you wish to have a picture or other HTML in your signature, continue to next step.
    1. Enable the checkbox "HTML signature". (4)
    2. Click on the “Source code” ( < > ) button in the top bar of signature HTML editor.
    3. A new modal window will open. Add your HTML code. Click OK when you're ready.
11. Click on the "Save" button. (5)
    

I'm using SOGo

Here is a short description of how you can add a signature in your emails in СОГо mail client.

Note that this signature applies only to mail sent with СОГо. Signatures for emails sent by third-party clients need to be configured in that particular client.

1. Login to your mail account with current credentials using SOGo: mail.svenskadomaner.se.
2. Click on the preferences icon next to your name in the left sidebar.
   
3. Click on the tab "IMAP Accounts" under Mail settings.
   
4. Click on the pencil icon next to your account to add desired signature.
   
5. Click on the "Save" button.