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Thunderbird will not send all messages in outbox

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I'm using Thunderbird 10.2.3.3 under Windows 10 Pro, and have put 50 messages in the Outbox with the "send later" option in the Mailmerge add-in. Each message has a pdf attachment of 170kb.

The "Send unsent messages" instruction only sends 15 (sometimes 12-16) messages before stalling, with the "Send unsent messages" option greyed out; however, the programme itself doesn't freeze, and there are no error messages. If I close Thunderbird and restart it immediately, I'm correctly asked if I want to send unsent messages - agreeing releases another 15 emails from the Outbox before the cycle starts again. Repeated closing and re-opening the programme eventually clears the Outbox, with each transmitted message correctly appearing in the "Sent" folder.

I last conducted a similar, limited mailmerge 4 months ago, using the same outgoing server settings, similar messages and attachment - on that occasion I had no problem sending 50 messages from the Outbox.

Any ideas?

I'm using Thunderbird 10.2.3.3 under Windows 10 Pro, and have put 50 messages in the Outbox with the "send later" option in the Mailmerge add-in. Each message has a pdf attachment of 170kb. The "Send unsent messages" instruction only sends 15 (sometimes 12-16) messages before stalling, with the "Send unsent messages" option greyed out; however, the programme itself doesn't freeze, and there are no error messages. If I close Thunderbird and restart it immediately, I'm correctly asked if I want to send unsent messages - agreeing releases another 15 emails from the Outbox before the cycle starts again. Repeated closing and re-opening the programme eventually clears the Outbox, with each transmitted message correctly appearing in the "Sent" folder. I last conducted a similar, limited mailmerge 4 months ago, using the same outgoing server settings, similar messages and attachment - on that occasion I had no problem sending 50 messages from the Outbox. Any ideas?

All Replies (5)

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This seems more a network performance issue, not a Thunderbird issue. It may also relate to any policy of your email host on allowing mass mailings.

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Thanks for your quick response, Dave. But the email host (NamesCo) has just confirmed that I have not hit any policy restrictions imposed by them, and that my outgoing server details are correct.

What sort of network performance issue did you have in mind? My broadband provider (Plusnet) is not showing any problems, and upload / download speeds are normal

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Forgot to add - the fact that when I close down Thunderbird and restart straight away, it immediately allows me to send another 15 messages or so, again suggesting that I've not hit any traffic / timing limits

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I have no answers for you, only awareness that such issues as yours require lots of tests, such as sending without attachments to assess any traffic delays.

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OK. Thanks. And apologies for mis-typing your name!

As a matter of interest, I've just sent 35 messages with the same attachment via a different outgoing server with no problem at all, suggesting to me that there are no particular traffic delays. The main differences I see between the two servers are the connection security and authentication - none in one case, SSL/TLS + Normal password in the other.

So I'm mystified!