Try these suggestions:

Do you scan outgoing emails as this can slow the process.

If yes, then access your Anti-virus pproduct and switch off scanning of incoming and outgoing emails. Thunderbird does not auto display remote content and any attachments you open will still be scanned.

re; synchronising subscribed folders:

you can specify that only xx amount is downloaded. This should be easier than synchronising the total folder. tools > Account Settings > synchronization & storage synchronise the most recent xx days. see info here;

• https://support.mozilla.org/en-US/kb/imap-synchronization#w_configuring-synchronization-and-disk-space-usage

After synchronising, go into offline mode. When composing emails make sure you are in 'Offline' mode and use the 'Send later' option to store emails in 'Outbox'.

then go into online mode right click on 'Outbox' and use the 'Send unsent messages'.

Offline: click on 'two blue screen icon in bottom left Status bar. It will change to two black screen icon when in offline mode.

Online mode: click on 'two black screen icon in bottom left Status bar. It will change to two blue screen icon when in online mode.

Hello Toad-Hall, Thank you very much for taking the time to help me. I thought I would leave the reply a few days to see how it was performing. I have disabled incoming and outgoing email virus scanning and this does seem to give perhaps a 20% improvement but does not entirely solve the problem. Unless I misunderstand, the other points are perhaps not so relevant. Costs for actual time spent online and data transmitted are not an issue as this is allowed for by some one else, it is just the speed and efficiency of the synchronisation that is holding me back so I haven't used the Offline/Online options. When TB synchronises a folder is it reviewing the entire folder contents so that having everything there is actually giving it more work to do? If this is the case perhaps I can move all the history to a local folder and then only synchronise the last 30 days? I have already downloaded all emails from my google account so I am just keeping up to date. I really need to be able to refer to my full email history. I notice that the authentication and handshaking between TB and the server happens multiple times. For instance, when I send a message, and then again when the sent message is copied to Sent items. On a fast, low latency connection I assume this happened so quickly I never even noticed, but in this situation I wonder if this is absolutely necessary. I am thinking that as the Google Webmail app does not struggle in the same situation, TB is working differently, but does it need to? Regards Dominic

As you probably know TB works fastest with small compressed inboxes.

Moving mails from Inbox to local folders works fine IF you keep a backup on another disk (external) Moving mails to another folder on server keeps Inbox small and easy to synchronize. BUT open your other folder takes more time as you then have to synchronize a large one.

Either way compressing folders is a must.

Synchronised subscribed folders are constantly updating server folders and vis versa. So, keeping your folders small will help. Moving old emails off the server into 'Local Folders' mail account will mean you still have access to them. They are now stored in 'Local Folders' on your computer, so do not synchronise with server.

Setting the synchronising to eg: 30 days, means the synchronisation will only check and download last 30 days rather than checking the whole folder. Defiantely should help your situation.

Many imap mail accounts have an idle command that works in the background. The IMAP server notifies Thunderbird when there is new mail by sending a command over the existing TCP-IP connection, rather than checking every xx minutes.

I agree with gnospen: Compacting folders removes 'marked as deleted' emails which are hidden, but still take up space. Compacting should be done on a regular basis, especially in Inbox and Junk folders as they get more activity.

re :Google Webmail app does not struggle in the same situation. If using the webmail account - Those folders and emails are on the server and are not being synchronised with any email client program on your computer, until you access those folders via an email client such as Thunderbird. But you have to have internet connectivity to read them.

It depends upon how you want to see and have access to emails. If you travel about and need access to emails via webmail. phone, other computers etc, then having them all able to synchronise will be useful, so IMAP would be a good option.

If you really only view emails from the one computer and sometimes use webmail if not at home, then POP may work better as it doesn't do all that constant synchronising every time you move an email.

Info on POP mail account. You would have to check that POP forwarding is available and selected via webmail account options. Pop mail accounts only get access to the server Inbox. They download anything not previously downloaded from the server Inbox to the pop mail account. You can set up how often it checks the server. All of those downloaded emails are stored on your computer. Usually, pop mail accounts download to Thunderbird and delete the copy off the server, but you can set up the mail account to 'Leave message on server', so that you can also see new mail via webmail.

As Pop mail accounts cannot see anything other than server Inbox, you would need to get all your mail into Local Folders. Synchronise folders, go offline, copy to Local Folders, then check they copied over ok. Then you can choose to delete those emails off the server and remove the imap mail account. Create a new exisiting mail account and make sure it's server type is POP. check Account Settings to make sure you 'Leave message on server'. From then onwards any new mail arriving in server Inbox will get downloaded to Thunderbird pop mail account.

I'm not saying you have to have a POP mail account, but it may be another option you could try.

Hello Toad Hall and Gnospen, Thank you both very much. Very interesting and this helps me understand how this is working. I'm going to do some more experimentation with all your suggestions and see what works best. I'll let you know the results but this may not be for a few weeks. Regards Dominic