I have implemented an IMAP server and I am facing the following problem:

There are some mail clients (Apple) that close a connection after 60 seconds. When a COPY command is received with a large number of mails, this command takes longer than 60 seconds on the server side. After 60 seconds this mail client closes the connection (I have seen the FIN in the TCP stack) and when the server tries to reply with a SUCCESS, the client is already gone.

After some time the mail client sends the same command and the same thing happens again.

I already tried to send a tcp keepalive without success. Has anyone an idea what to try next?

CodePudding user response：

You should be able to send an untagged OK response at any time. This may work as a keep alive:

 * OK Working on it...