C# IMAP 客户端 - 与邮件服务器的多个连接

Question

After experimenting with many IMAP API's, I have decided to write my own (Most are memory hogs, some just do not work, out of memory exception etc etc etc).

Anyway I have wrote some code that works (using TCPClient object) and its good so far. However, I want my one to be able to handle multiple requests to the mail server. For example: Say I get a list of all the UIDs, then I cycle through this list getting what I want (Body, Header, etc) for each message.

The question is, how would I handle, multiple requests at the same time? So instead of looping through the UIDs one at a time I can instead process 10 at a time.

What would be the best approach here? An array of TCP Clients, each with its own thread?

Thanks.

Answer 1

In general it's recommended that IMAP clients only have at most one connection to the server at all times. Not only does additional connections require valuable resources on the server but more important the IMAP specification does not guarantee that two connections can select the same mailbox at the same time. Relying on this capability being present on the server may render your client incompatible with those servers.

Instead you should use the protocol as efficient as possible. Note that many commands can operate on a set or range of UIDs. This allows you to make one singe request where you specify every UID instead of making one request for each UID separately.

Another good practice is to not request more data than what is currently needed. For example say that you have a list of messages. Then don't request detailed information for all of them, only request information for the messages that are currently visible.

I highly recommend that you read RFC 2683, IMAP4 Implementation Recommendations . It covers this among other things.

If you decide to use multiple connections anyway then a good approach is usually to use asynchronous operations and not use individual threads explicitly. Combination with some kind of run loop integration is often useful as well, that way your code is called when there is data to read instead of you code having to poll or explicitly check for it. This is often a good approach even if you're only using a single connection. Keep in mind that according to the IMAP protocol the server may send you responses even when you have not explicitly asked for them.