[SOLVED] Can't send mail after upgrade

I've just upgraded from version 5.0.5 to 5.0.10 on ubuntu 6.
Since that upgrade, mails can't be sent anymore.
When trying to send an email from the webinterface, the following error appears:

Code:

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A network service error has occurred. msg: system failure: MessagingException
code: service.FAILURE
method: SendMsgRequest
detail: soap:Receiver
trace: btpool0-13:1223295404941:1b5e41bd7a844aac

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Before the upgrade, everything has worked for months.
"zmcontrol status" shows that all services are running.
"tail mailbox.log" shows:

Code:

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com.zimbra.cs.mailbox.MailSender$SafeMessagingException: Connection refused; chained exception is:
        java.net.ConnectException: Connection refused

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Please, can anybody help me with this?!
Very much thanks in advance!

OK, my colleague was smart enough to help me remember I'd changed the SMTP port to 26 before the upgrade, which gets lost when upgrading. So the webinterface tried to send through 26 while it wasn't listening on that port.