Messages stuck in "delivering" status in AE

Dear Experts,

I have Idoc to file(EO) scenario. Sometimes, messages got stuck in "delivering" status and after that thousands of messages start pilling up in "To be Delivered" status. As, PI shows connecting to FTP server. This can happen anytime in a day and after PI server restart it get resolved.

I have checked various discussions on scn. Many people faced the same issue.I am unable to find the reason why at a certain point of time PI loses the connectivity and how to correct it or how to cancel/restart the messages in Delivering status without restarting PI server.

Please help.

Thanks in advance!

Regards

Danish