I have recently moved my website from a shared Linux server to a dedicated Linux server (Plesk Parallels Panel & Roundcube Webmail).
I have updated all paths etc so that FormMail works on the new server.

I normally access my emails using Entourage on Mac. My HTML emails (using HTML templates) used to come through with no problems. After I have moved the site though I no longer receive HTML emails. The message I get is plain text and preceded by the standard FormMail text stating:

(Your mail reader should not show this text. If it does you may need to upgrade to more modern software.)
If I check the same email using Roundcube webmail then I see the HTML email.

I don't understand why this is happening. The only thing that has changed is the server so surely this has nothing to do with my email reader (entourage). I can still view other HTML emails in Entourage.

Any help would be appreciated, thank you.