I am sorry to be pessimistic but I have experienced the same problem with FM Pro Advanced 11 and cannot send an email via either of our SMTP servers.
I have analysed the port traffic which indicates unexplained behaviour by FILEMAKER and reported it as an issue this week but have had no response from FILEMAKER so I cannot see where the problem lies exactly.
The MAILIT plug-in works with both our SMTP servers, but of course that is using separate independent coding.
thank you for your answer, good to know that I am not the only one.
This is a huge problem, there must be a solution.
I was trying out the Mailit plug-in that you mentioned.... this is interesting and gives you more options etc, but you cant just find a contact in your DB and select to send him an e-mail like you are supposed to be able to do from FM Pro, here you have to import contacts.
Hope that somebody have a solution to this
Good to know I am not the only one as well running into a problem sending email through Filemaker. I hope this does not take the FMP developers almost a year to fix like the printing problem they had when Filemaker 11 first came out and that issue wasn't fixed until the v11.03 patch came out.
I am wondering if I should downgrade to Filemaker 10? Does this problem exist in version 10 as well?
There's also another issue with SMTP emails that may affect your recipient's ability to get the email without it being filtered out by anti-spam filters.
For More Information see: Email header malformed when using SendMail
This is one of many acknowledged bugs that can be found in the Known Bug List here in the Report an Issue section of the forum.
It can also be downloaded as a database file from:   http://www.4shared.com/file/8orL8apk/FMP_Bugs.html