Your message was sent, but an error occurred during post-processing.

When sending a message Evo gives this error:

Your message was sent, but an error occurred during post-processing.
The reported error was "Failed to append to INBOX/Sent: Error appending
message: Stream has outstanding operation
Appending to local 'Sent' folder instead.".

This account is set up with IMAP, previously in version 3.10 this error did not
occur.

This bug has been reported to Gnome, https://bugzilla.gnome.org/show_bug.cgi?id=737733 and has a patch written for it. However I've been advised to contact the Ubuntu maintainers about getting the patch applied. This is noted on comment 19 of the above bug report.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: evolution 3.12.6-1ubuntu1~trusty1 [origin: LP-PPA-gnome3-team-gnome3-staging]
ProcVersionSignature: Ubuntu 3.13.0-38.65-generic 3.13.11.8
Uname: Linux 3.13.0-38-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.5
Architecture: amd64
CurrentDesktop: GNOME
Date: Mon Oct 20 21:17:56 2014
InstallationDate: Installed on 2014-07-13 (100 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
SourcePackage: evolution
UpgradeStatus: No upgrade log present (probably fresh install)