Socket Error when sending mail from Webmail (Horde, etc.)


Active Member
Nov 5, 2003
I get the following error when trying to send mail from Horde or other webmail programs:

There was an error sending your message: Failed to set sender: [email protected] [SMTP: Failed to write to socket: not connected (code: -1, response: )]

I have searched and found two suggestions - one is to enable SMTP_ALLOWLOCAL in CSF (which was already enabled with a "1"). The other suggestion was to ensure the Horde Identity had a valid email from address. I set the email address and this still has not resovled the problem.

I tried completely disabling CSF to see if it was something caused by the firewall, but that hasn't helped.
I have done a cPanel upgraded, checked SMTP settings in Tweak Settings and checked Security levels, but nothing has resolved this.

Has anybody got an idea where I should look next?


Quality Assurance Analyst
Staff member
Oct 2, 2010
somewhere over the rainbow
cPanel Access Level
Root Administrator
Was MySQL upgraded or downgraded recently on the machine? There are reports in our ticket system where a MySQL downgrade caused this to occur with Roundcube. I'm trying to determine if this might be the same cause.