There are several reasons which can cause this problem.
1st possibility :
If you have copied / pasted your message from Microsoft Word or a third-party software, some special characters may have been added to your message.
In order to correct this display problem, you must delete the whole formatting of your message.
This is how you must do it :
2nd possibility :
Your message is correct but, during reception, the accents appear as special characters.
In general, emails are edited with UTF-8 encoding.
Our Mailpro Editor uses this encoding for your messages.
Therefore, the issue does not come from your message but from your addressee's income box.
Your contact must change his email client's display mode (Outlook, webmail, Thunderbird, Mail …).
This is how he must do it :