[Exim] Return code from EXPN

Hello,

When Exim 4.05 refuses an EXPN, it returns a 550 code. Since 550 usually
means something like 'mailbox not found', is 550 the most appropriate code?
Sendmail, qmail and postfix all seem to return 502. Should Exim do the same?

Thanks
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and men and dogs should relax and get used
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