Enigmail cannot communicate with gpg-agent

Thanks so much for everyone's detailed input on this issue.

I have a similar problem since my system updated to Enigmail 1.9 on Feb 25. I fixed the problem by uninstalling Enigmail 1.9 and switching to 1.8.

For me, this was easy since I use Debian 8 and I simply uninstalled Enigmail as a standalone addon and replaced it with the debian main repo's rendition of Enigmail (which, some research shows, happens to be version 1.8.2). Shrug. Have had no problems since that change. I hope that's useful to others and thanks again for putting me on the right track to solving the issue.

While the answer of thisthatother only shows how to solve it on a Debian system, the approach is the same:

Downgrading.

Since Enigmail released version 1.9 on February the 23rd and the problems started from that day on, the only three solutions are:

1. Wait for Enigmail to sort things out and install their update to the 1.9.x and stop using encryption until they provide the update
2. Dig around and solve the problem yourself (which not everyone is capable of doing due to limited knowledge of the underlying software architecture)
3. Downgrade to 1.8.2, then wait for Enigmail to sort things out and upgrade to a 1.9.x that solves the error that occured with 1.9.

I can't help with 1 or 2, but with number 3:

• Download Enigmail 1.8.2, which is the latest pre-1.9 version that didn't introduce the error
• Uninstall Enigmail 1.9 through the Thunderbird Add-ons menu
• From within that same menu, manually install the downloaded 1.8.2 file by clicking on the Add-ons configuration button at the top of the Thunderbird Add-ons page, left from the search text entry field
• Restart Thunderbird

It should now work as before the update to Enigmail 1.9.

I would suggest to disable automatic updates for Enigmail until this bug introduced in 1.9 has been sorted out. You can disable them by clicking on the "more" Link that's in the description text of the Enigmail extension in the Thunderbird Add-ons page.

No need to downgrade enigmail plugin :

• List item
• Ubuntu 16.04
• Thunderbird 45.2.0
• Enigmail 1.9.5
• gpg (GnuPG) 1.4.20

In a terminal :

killall gpg-agent
export GPG_TTY=$(tty)
gpg-agent --daemon /bin/bash

( --use-standard-socket is obsolete)

No need to restart Thunderbird.