Unexpected behavior with Notifications or Issue Creation via Google Apps
Emails are sending or receiving slowly.
Do you use Google Apps for your email?
If yes, check your actual traffic vs Google's limits as described below.
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.
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.