Why do I get timeout problems with Thunderbird and Sendgrid?

Question

I am helping my friends sending a newsletter (1000 recipients) using Thunderbird 7.0.1 and the Mail Merge plugin.

For the SMTP provider we are using Sendgrid.

Mail Merge plugin nicely splits the messages into individual ones and starts sending them, but they are having timeout problems with the SMTP server.

Do you have any idea why is this happening? Is Thunderbird trying to send all the mails in it's outbox at once? I hope it is not the case. Is there any way to control how is Thunderbird processing it's queue? Is there any plugin for Thunderbird to control this behaviour?

Answer 1

My problem was with Sendgrid indeed, and the solution was to use their X-SMTPAPI header instead of just sending messages with Bcc: or sending individual messages from Thunderbird. Using their own header, the processing of emails worked perfectly and it was enought to send one message only.

Answer 2

Your issue sounds to me like it is on the SMTP service side, not Thunderbird.

Sendgrid should have no problem with 1000 emails at once through their SMTP service.

I use Elastic Email SMTP Relay and have had no issues. Maybe try another service like Elastic to test where your problem lies. Elastic lets you send 100/day up to 1000 emails for free, so it would be a cheap way to test this.