This is probably fixed with the latest changes how OTK and session
management are handled with a separate cursor.

Another reason for concurrency problems might have been a mail setup
that runs the mailgw inside the delivery system of the MTA, so that
concurrent MTA invocations will produce concurrent roundup mailgw
invocations. This is generally not a recommended setup for several reasons:

- concurrency issues if several mails referring to the same roundup
  issue are sent in close succession (as is the case in this issue)
- it is hard to disable mta delivery during updates or maintenance of
  the roundup tracker

the recommended setup is a mailbox where the MTA delivers mail and a
separate job that fetches mail from this mailbox via POP or IMAP
protocols. In that case delivery in the MTA and processing of the mails
by the roundup mailgw are decoupled, no concurrency issues will arise
and it is easier to upgrade or disable the mailgw during maintenance
periods.