E-mail's I send are crashing peoples Systems/Devices

Question

My e-mails are crashing other people devices/systems be it, iphones, pc's or mac's.
My partner on the same server is not having this problem. I have also contacted my server provider and they have not had any other problems reported.
Is there a virus scan I should be running?
Any other suggestions would be greatly appreciated, this is starting to hinder work as people are not willing to try and open my e-mails anymore as there systems just crash.
Any Ideas????

Answer 1

After seeing one of the e-mails in question, I think I was able to locate the problem. Hopefully the original poster will be able to confirm this.
Apple Mail seems to have created a very complex HTML e-mail message. This may have been caused by copying a signature from another program like Word. While Apple Mail can display such a message, it would not surprise me that PC e-mail programs couldn't handle it.
Here is but a tiny sample of a 6-line message with 2-line signature. There is actually much more to this section, but I didn't want to paste all of it in here. Keep in mind there is no actual content.
<br></font></div></span></i></span></font></span></div></span><=
/font></i></b></span></span></font></i></b></span></font></div></span></fo=
nt></i></b></span></div></span></font></i></b></span></span></font></i></b=
></span></font></div></span></font></i></b></span></div></span></font></i>=
</b></span></span></font></i></b></span></font></div></span></font></i></b=
></span></div></span></font></i></b></span></span></font></i></b></span></=
font></div></span></font></i></b></span></b></span></div></span></font></i=
></b></span></span></font></i></b></span></font></div></span></font></i></=
b></span></div></span></font></i></b></span></span></font></i></b></span><=
/font></div></span></font></i></b></span></div></span></font></i></b></spa=
n></span></font></i></b></span></font></div></span></font></i></b></span><=
/div></span></font></i></b></span></span></font></i></b></span></font></di=
v></span></font></i></b></span></b></div></span></font></i></b></span></sp=
an></font></i></b></span></font></div></span></font></i></b></span></div><=
/span></font></i></b></span></span></font></i></b></span></font></div></sp=
an></font></i></b></span></div></span></font></i></b></span></span></font>=
</i></b></span></font></div></span></font></i></b></span></div></span></fo=
nt></i></b></span></span></font></i></b></span></font></div></span></font>=
</i></b></span></div>
I see no evidence that the original poster did anything wrong. My suggestion was to delete the old signatures and recreate them using only Apple Mail. Doing that reduced this 6-line e-mail from 52K in size to 4K in size.
The moral of the story is to avoid pasting styled text from elsewhere into Apple Mail. If you must, use "Paste and Match Style" to strip out any formatting and paste in plain text. There is nothing wrong with just using paste, but it could render your message unreadable on PCs and may even crash them. With a little patience, you can create very nice looking signatures in Apple Mail. Here is one example - there are many more: http://smokingapples.com/miscellaneous/html-signature-apple-mail/