Can receive e-mails through Thunderbird but not send them

Can receive e-mails through Thunderbird but not send them

For about a fortnight now, I have been unable to send e-mails through Thunderbird using Zoho-hosted accounts. None of my SMTP settings (of which I have attached a screenshot) have changed—I’m just suddenly unable to send mail except through the Zoho webmail portal. This is true for both my individual company e-mail address and the company’s client services e-mail address.

I have also attached a screenshot of the error I get when attempting to send mail through Thunderbird.

I use a VPN and change servers daily. Although I have been sending mail over the VPN without issue for a couple months now, I wonder whether Zoho finally decided to prevent my VPN’s IP addresses from sending mail through Thunderbird?

This issue greatly hinders my ability to do my work. I depend on the ability to manage a great many e-mail addresses in the Thunderbird client, and having to log in to Zoho webmail—let alone into either of two different webmail accounts depending on whom I’m replying to—just to answer an e-mail is a major source of delay in my work.

I have to say that I have encountered more issues with Zoho Mail than I have ever experienced with any other e-mail service. I heartily wish my company had picked another provider—and indeed the topic of a switch has already been broached this week, and not by me.