Unreadable mail message

I sometimes get unreadable mail messages in my Mail app looking something like below.
The sender can be workoing from both a PC or mac, so that is not the issue.
Making Mail using only plain text doesn't help.
I am using IMAP via Gmail.

Sometimes the content of the mail shows up fine, but then i don't see the header with From, Subject, Date etc. info. The whole headerpart is just gone.

This is how the content sometimes look:


------= NextPart_000_009A01CBD35E.41736820
Content-Type: multipart/alternative;
boundary="----= NextPart_001_009B01CBD35E.41736820"


------= NextPart_001_009B01CBD35E.41736820
Content-Type: text/plain;
charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable

Hej,

=20

Den mouseover effekt du taler om. Skal det bare v=E6re en standard en, =
f.eks
farve skift eller underline.

=20