I'm unable to send any email through Thunderbird using Zoho due to a login failure. 

Email is still coming in just fine, but the SMTP is failing. 

I am using 2 factor Auth with an application specific password (I have since regenerated that password and the issue still persists). 

The SMTP settings are correct and IMAP is enabled for my account. 

Sending email wasn't a problem as little as a week ago, but seems to be an issue now. 

Did something change?