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Emails are extremely slow to send & hang then unable to send. (Windows)

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I have had a lot of problems with Thunderbird lately. I have tried a complete re-install, logging out and back in again, changing passwords and settings but it's not been working right for about two weeks.

First of all, all of my emails wouldn't load when clicking on them, they only displayed the subject in the overview browser. I had my settings as 'downloaded for offline viewing' so I tried making my settings so they weren't available for offline which worked for a bit but some messages took far too long to load, appox 3-5 mins per message. I then re-enabled for offline use and my mailboxes took about 5 days between 9am-6pm to download, each time only managing between 200-400 messages out of 21000 (I am working as a business) before I got a notification saying the server couldn't complete the task due to being under heavy load. Once this eventually completed, everything was fine for a few days but it started acting up again so I reverted back to online use only which again, worked fine for a few days and now most or if not all of my outgoing emails hang and struggle to send, most with the error - Sending of the message failed. The message could not be sent because the connection to Outgoing server (SMTP) was lost in the middle of the transaction. Try again. Or - connection timed out

I have also had issues with sending emails from my phone with attachments (pictures) where they just sit in the outbox not sending or doing anything, they don't have the red '!' like when there is an error which is puzzling and sometimes the emails show up days later.

I have tried speaking with my email provider (Ionos) and they were very unhelpful, I checked all my settings and details with them and they advised that nothing is wrong on their end.

Can someone shed some light on this and help me as I am at my absolute wits end with this! Any suggetions or help would be greatly appreciated, I have uploaded some of my thunderbird settings which may help. I really want to get this sorted as I enjoy using Thunderbird but at this rate, I am going to have to remove it completely and go back to Outlook.


Attached screenshots

Modified by Wayne Mery

All Replies (6)

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As problem is with phone and computer, it sounds more like your internet server connection is being over worked and struggling to keep up.

Image shows you have a setting that says 'Check for new messages every 1 minute'.

Strongly suggest you change that setting to 10 minutes minimum or even 15. You already have a setting for server to notify when new message arrive. It is also possible the server uses IDLE in which case the email may be pushed.

"Push e-mail" means that when a message is delivered to the mailbox you want to get immediately notified of it. Thunderbird provides that if your IMAP server supports the optional IDLE command. The IDLE command eliminates the need for a e-mail client to poll for new mail - the mail server automatically notifies the e-mail client whenever there is new mail."


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Do you compact on a regular and frequent basis ?

I notice the information in image supplied says you do not clean up (expunge) Inbox on exit. Account Settings -> Server Settings -> Clean up ("Expunge") Inbox on Exit "

'Clean up(Expunge)Inbox' means it compacting the Inbox to remove all old hidden marked as deleted emails. So reducing the file size and helping to keep a healthy Inbox folder.

Not compacting the Inbox folder often enough may cause performance problems. Deleted messages aren't physically deleted until the folder is compacted, so for example Thunderbird might be loading a 100MB folder index when it displays a Inbox folder with just a few messages.

I suggest you compact any folder that gets a lot of moving of emails or deleting of emails, such as Inbox, Drafts, Junk etc. Also set up Account Settings to Clean up on exit and set up an auto compact

To manually compact, right click on folder and select 'Compact'.

You can also set this up to occur automatically in this location:

  • Menu app icon > Options > Options > Advanced > 'Network & Disc Space'


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Anti-Virus products can also slow down performance eg: scanning each email before it is sent, scanning a file or folder when it is accessed.


You can test by auto disabling Anti-Virus, but do it by restarting the computer in 'Safe Mode with Networking' option and then starting Thunderbird and see how performance improves. This will tell you if the Anti-Virus is badly influencing Thunderbird performance.


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Check proxy settings as making a connection through a proxy can slow startup performance. Normally there is no reason to use one unless you are making a connection through a VPN or your ISP requires it.

  • Menu app icon > Options > Options > Advanced > 'Network & Disc Space'
  • Under 'Connection' section
  • Click on 'Settings'
  • Suggest you use: 'Use system proxy settings' or No Proxy'.


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Thanks, I have used these settings and will trial it this week to see if they make any difference and report back next week!


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Still having issues sending emails with attachments from PC as well as iphone, surely these fixes above wouldn't affect that?


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