Because of restrictions in the front-end computers of the helsinki.fi mail system, the mail delivery from the cs.helsinki.fi mail to helsinki.fi mail has been sometimes slow.
The receiving side has been refusing to accept incoming messages and the sending side has been forced to retry sending the mail, at worst, even dozens of times. The retransmissions make the situation even worse because they increase the load of the front-end computers and the delivery of the mail slows down even further. This applies as well to directly sent messages, to mailing lists as to forwarded messages. The problem occurs with Office365, Mappi, and Unix mail addresses. Delays have been, at worst, several hours.
The problem has now been solved by rerouting the mail before sending it to IT Center computers through a special flow control host which dispenses mail to helsinki.fi front-end computers at a more appropriate pace.
The solution has now remedied the problem, but it should be noted that this applies only to mail that passes through the mail system of the Department of Computer Science.