Evolution does not send Emails with an attachment

I suggest you report a bug

A bug report was sent, as suggested.

I had this EXACT same problem. It turns out that Evolution's "Restore" function did a sloppy job this time -- with serious impact on my business, as it's taken me a couple of weeks to realize that I had a problem. The Backup and Restore has always been one of the best features of Evolution, but when I upgraded to 15.04 (a clean re-install), the Restore function let me down.

The fix here is that if you have Evolution open, go to Edit/Preferences. Select your e-mail account -- in my case, a POP account. Click on "Edit", and the Account Editor will pop up. Click on "Sending Email" (on the left). If your account settings are like mine were, it will say "No encryption". Change that setting to "STARTTLS after connecting", then click "OK", then close the "Evolution Preferences" window. (This SHOULD have been taken care of when you restored Evolution, but it looks like somebody dropped the ball.)

Now e-mails with attachments will send correctly. YOU SHOULD PROBABLY GO BACK AND RE-SEND ALL OF YOUR E-MAILS THAT HAD ATTACHMENTS, if you did not already re-send them with another e-mail program. This will be a nuisance to your recipients, but what else can you do? Your e-mails without attachments probably do not need to be re-sent.

I also had a problem with my Contacts file, but I can't remember the details. I know that I did find a cure online.

Thank you for your response. The encryption settings were edited as above.
The following message was received while trying to send the email:-

An error occurred while sending. How do you want to proceed?
The reported error was "Failed to connect to SMTP server auth.slt.lk in secure mode: STARTTLS not supported".

I have stopped using Evolution and have installed Thunderbird as it is also the default email application.
Hence this question may be closed.

Thank you.