There is currently an issue with our webmail interfaces at https://webmail.webfaction.com and https://squirrelmail.webfaction.com/ which is resulting in sporadic 500 Internal Server Errors for some email users.
We are currently looking into the problem and hope to have normal service restored soon.
If you need to access your mailbox, please consider https://docs.webfaction.com/user-guide/email.html#configuring-an-email-client until this issue is resolved.
We will update this entry as soon as we have more information.
Update 2018-12-12 14:48UTC: We applied a patch to our webmail instance a few days ago and haven’t seen an issue since, so we are going to go ahead and mark this as fixed. Feel free to raise a ticket if you are still experiencing issues.