The MAX Mail engineering team has been investigating intermittent delays with outbound mail, on Tuesday and Wednesday of this week, that have affected some customers, primarily in North America.  These delays manifested in the connections from the outbound sending server at the customer site to the outbound servers at MAX, during the envelope phase of the SMTP conversation, rather than within the message processing or message delivery process at MAX after the messages had been accepted.

We believe we have isolated the cause — a software bug in the message acceptance code related to handling of outbound NDR messages.  The related code under certain conditions caused the introduction of delays in the processing of other outbound messages from that domain.

A temporary workaround was deployed on Wednesday morning Pacific time, and an updated code base is being deployed today.  No further problems have been reported or seen in our monitoring since the temporary fix on Wednesday.

We apologize for the issue and any inconvenience caused during that time period.