how to limit email download to 20 mails (at a time)?

[chrizoo]

It seems you are looking at a niche requirement for which neither the POP nor IMAP protocol offers a solution that matches you intended procedure.

This is not a protocol problem, but a software problem:

I don't remember anything in the rfcs that would prevent [that]

mail accounts don't have a get next 500 message feature is because few users get thousands of messages every day

Some do. But that's not even the scenario I was describing.
I'm talking about any scenario in which a user has not downloaded his/her messages for some time. There can be dozens of different reasons for that:

• User was away all summer long on vacation. Or 6-12 months study abroad (where he uses webmail). User comes home, starts PC and is submerged by 12 months worth of messages.
• User reactivates an old eMail account (access was lost due to hardware failure or lost password, etc.)
• etc.

Taking into consideration millions of Thunderbird users worldwide, this affects many people. In fact all Thunderbird users are affected, who want to retrieve their eMails after an extended period of time.

[mgagnonlv]

I don't see how you can do exactly what you are aiming for. The scenario I would suggest to you is relatively close to that, functionality wise.

• Preferably set your account as IMAP. It leaves a backup on the server and also allows you to access your emails from various platforms: Thunderbird (home and/or office), phone, web interface, etc.
• Unless you have access issues, use (I think) the default parameters to download everything.
  (Note: my menus are in French, so I might not have the exact names)
  Right-click on the account name, go to "Server Parameters" and check (in the middle):
  – check mail at startup (checked)
  – Check new mail every 15 minutes (checked)
  – Authorize instant notifications when new messages arrive (checked)
  Then under "Synchronization and disk space", select :
  – Sync all messages regardless of age
  – No not delete any message
• Use Thunderbird normally.
  As you said, you might receive a ton of messages, especially if you went on a 6-month holiday or receive lots of mail.
• Use the "zero-inbox" strategy. When you process a message, always move it to a different folder. You could create many folders; for example: Work; Administration; Personal; Inbox-processed
  In other words, you always move a message you have processed somewhere else: either in a specific folder or in garbage. That way you know that any mail left in the Inbox has yet to be processed.

[tanstaafl]

Using a IMAP account that only downloads headers to the hard disk (due to both disabling offline folders in synchronization&storage and disabling global search/indexing) is your best solution if you have tens of thousands of messages in a folder because it adds the least overhead. Its also unaffected by the size of any of the messages.

With tens of thousands of messages in a folder you can't afford the time to go through them one by one. With a IMAP account you can use the quick filter toolbar to search for groups of related messages that you can delete without having to individually read them. The searching is done by the IMAP server, NOT by Thunderbird. That is important as it avoids the need to fetch the contents of all of the messages and build a search index beforehand in order to search all of the messages.

Another advantage is it avoids the potential problems of a POP account having a logjam if it can't download a message, and not being smart enough to report the error and skip over it to the next message.

I don't know the maximum number of messages that you can effectively have in a IMAP accounts folder (configured to only download headers) without the performance being unbearable but that limit is much higher with that configuration than with a POP account. Webmail can also handle having lots of messages (i.e. it scales well) but it normally doesn't have a user interface that is suitable for searching that many messages.

Don't overlook the possibility of using a virtual folder (aka saved search) with a IMAP account to break the inbox into chunks that you search in. A virtual folder doesn't actually move any messages, its just using smoke and mirrors to create a folder that acts as if it contains just the specified messages. For example you could specify the virtual folder contains all of the messages in the inbox that were sent from yahoo.com. Then use the quick filter bar to search among them to find groups of messages that you want to delete (such as all messages for a specific distribution list or on a specific subject). When you are done with that chunk you replace the virtual folder with another one and repeat.

http://kb.mozillazine.org/Saved_Search

[tanstaafl]

You might find the expressions search / Gmail UI add-on at https://addons.thunderbird.net/en-US/th ... ui/?src=ss useful. It makes the quick filter toolbar more powerful.