I have the same problem, but only in plain text emails. Did you ever find a resolution to this?
Extra carriage return characters are added every line to plain text emails. This is particularly annoying with notifications of posts sent to subscribers via the subscribe2 plugin.
I think it is a problem of translation between unix and windows with carriage return / line feed. I’ve read this was an old problem that was fixed in wp_mail (interfacing with PHP mail) years ago. Apparently the fix never made its way into the SMTP plugin.
Here is the source code from an example email (via my mail client):
I recently came across a document that perfectly illustrates this last poin=
t: a=0D
power point presentation by a senior Federal Reserve Bank research economis=
t,=0D
given at a conference aimed at school teachers specializing in economics.=
=0D
=0D
The =0D is the quoted-printable mime for a carriage return character, which is interpreted by all mail clients (in conjunction with the new lines) as double line breaks.
