It would help if you added some info.

• What OS are you using?
• What version of Thunderbird are you using?
• What Anti-Virus are you using?
• Does your Anti-Virus scan folders?
• Does Anti-Virus scan incoming and outgoing mail?
• What ISP are you using?
• Is this a gmail account, if no what server are you using?
• Is this an imap or pop mail account ?

Perform a test: Restart computer in 'Safe Mode with Networking' Start Thunderbird. Do you still experience issues?

If yes: Start Thunderbird in Safe Mode.

• https://support.mozilla.org/en-US/kb/safe-mode-thunderbird

Do you still experience issues?

Please report back with info and test results.

Thunderbird is a free program and the people who help on this free forum are volunteers doing it free in spare time. They could be anywhere in the world. Each case may sound the same as another, but may not necessarilly be the same issue. If you could supply the above info then we can start to try to understand what is going on in your case.

thank you for taking the time to help! im using win10 and i assume the latest thunderbird i always run updates when i get notified,

antivirus is webroot i dont know how it operates and what it scanns etc,

I have 3 IMAP hosted accounts connected to website my domains and its not all accounts that have this problem. 2 are from crazy domains and one from netsell, usually its my one most used crazy domain account that has the problem. Its occurred a few times recently a lot more often. I'v extensively discussed this with the server tech support and everything they do always tests out fine, using their webmail log in is also fine, its only when i use thunderbird it does this.

The problem has gone away today as it mysteriously does so i cant perform tests at the moment and i have started using another client as i cant have this instability. It would be nice if i could get to the bottom of it somehow.

re :usually its my one most used crazy domain account that has the problem.

You cannot compare webmail as it is entirely different.

Items to check out:

First make sure you have subscribed to see the server 'Sent' folder. Right click on mail account in Folder Pane and select 'Subscribe' select the server 'Sent' and also 'Drafts' folder and click on 'Subscribe' click on 'OK'

Then check the Account Settings:

• Right click on mail account in Folder Pane and select 'Settings'
• select 'Copies & Folders'
• Select 'Place a copy in'
• select 'Other' and choose the 'Sent' folder on the imap mail account'

Drafts and Templates: section Keep message drafts in:

• select 'Other' and choose the 'Draft' folder on the imap mail account'

• click on 'OK

How large are your Folders ? Imap folders are synchronising with server and it is so much quicker if they are smaller in size. Do you have the 'Folder Pane Columns' enabled?

• Menu icon > Options >Options > Layout > select: 'Folder Pane Columns'
• Then enable the 'Size' column - see image below

Suggest you Archive older 'Sent' emails, so they are not cluttering up the 'Sent' folder. The 'Sent' folder can become quite large over time.

Do you frequently compact folders? When you delete an email, it is marked as deleted and hidden. When you compact the folder, it removes the hidden marked as deleted emails, cleaning up the file and creating space; so file size is reduced. This is particulary important on folders which get emails deleted. EG: Inbox, Junk, Drafts

Note: if you have not compacted in a long time, as a precaution, I would move or copy all wanted emails into another folder to use as storage. Then compact folder. If a folder becomes corrupted by a lack of compacting or by eg: an AV product scanning and 'fixing', the start and end of marked emails can be hard to determine and has been known to lose emails. Unfortunately, it is not always so easy to determine when a folder has become corrupted, but as you have experienced some slowdown etc issues, it might be a good idea to move good emails first. Please note that you do not usually need to do this especially if you compact on a regular basis. I delete quite a few emails each, so tend to compact some folders on a daily basis.

Info on compacting: http://kb.mozillazine.org/Thunderbird_:_Tips_:_Compacting_Folders

It is also possible that you have AV product scanning emails you want to send and so it is interrupting the process. If you had perfromed those tests I mentioned (Safe modes), then this could help to determine whether something is interfering.

Unfortunately, you usually discover the web support is webmail support and they are often not exactly helpful when it comes to imap via an email client.