Slarty's comments are interesting. I have seen e-mail servers almost grind to a halt, because of emergency content filtering to block particular virus attacks.

Some organisations get third parties to handle their external e-mail. This includes content filtering and AV scanning. Frequently they use up to four different AVs that are updated hourly. One of these will be a "heuristics" based scanner that looks for "new" viruses based on behavioural analysis.

This slows down your e-mail, but you so not "see" it, as it is happening remotely, and your local server is running "normally" particularly for internal e-mails. You could probably create this yourself if you separated internal and external connectivity.


Cheers