Thunderbird email from specific user is causing performance issues

Question

In our office we are using Thunderbird. One user in particular, when using Thunderbird, has issues with sending and receiving emails.

Whenever he sends an email, it takes 3 times as long to connect to the hosting site (hostpapa.com.au) to send the email, and the same for any user that attempts to send emails to him.

Additionally, we recently set up an auto reply on his account, and whenever I attempt to open the email from him, it causes my (and any other user's) Thunderbird to stop responding intermittently, until the email opens. This generally takes a few minutes.

This is the email that the auto-response generates:

This is a multi-part message in MIME format. --------------000102020002060902000107 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit I am out off the office until 5th Jan, and will reply to your email when I get back.

Sincerely

-User-

--------------000102020002060902000107 Content-Type: image/bmp Content-Transfer-Encoding: base64 Content-ID: Qk3uTkoAAAAAADYAAAAoAAAAXQcAAF0DAAABABgAAAAAALhOSgAAAAAAAAAAAAAAAAAAAAAA ////////////////////////////////////////////////////////////////////////...

The rest of the email consists of endless "/" (I could not copy the entire email into this window, it was causing performance issues in Internet explorer as well), with the occasional burst of numerical sequences that make no sense like:

4+Pj4+Pj4 +Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4 +Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4+Pj4 +Pj4+Pj4+Pj4+Pjx8fH4+Pj4+Pj

and:

8A --------------000102020002060902000107--

What is happening? What might be causing this?

EDIT I copied the email to a .txt file, and it was 6.7 MB

EDIT 2 I asked him to send me an additional, blank email (the auto-response email had been disabled at this point), it still took some time for the message to send/receive, but when I exported to .txt, the file was only 211 bytes.

Answer 1

Check to see if a corporate wide signature policy is in effect, if so, it might be tripping up on him. Additionally, check his mailbox and Remove and signature he may have added. Finally, ensure that he's using the same text encoding as everyone else. This smells like a signature or encoding problem to me.

Answer 2

Check the mail contents when he uses the webmail client - If his computer is infected the mail could be modified before being picked up by the SMTP server. Also, PDF binary files can get attached as text/html and it results in a gargantuan string that can take awhile to parse.

Dump any attachments from his signature, try to send a plaintext e-mail with webmail, and also, attach to the hostpapa.com.au SMTP server via GMAIL using his credentials. If gmail is workable, then it is likely the desktop that is generating the extra overhead.