症状

Emails are sending or receiving slowly.

診断

Do you use Google Apps for your email?
If yes, check your actual traffic vs Google's limits as described below.

原因

Google has a number of limits on their inbound: http://support.google.com/a/bin/answer.py?hl=en&answer=1366776&topic=28609&ctx=topic and outbound: http://support.google.com/a/bin/answer.py?hl=en&answer=166852&topic=28609&ctx=topic emails for Google Apps customers.

ソリューション

Outbound: Set up a local SMTP server with an SFP record (to prevent being marked as spam) to send outgoing emails. This will not count against your limits.
Inbound: Split up your mail handlers to use different addresses.