Tag: qmail

How to solve “550 sorry, user unknown” problem when using pd-admin

Recently, a client reported problems when trying to send mail to certain domains hosted on their own web server. The web server in question was running pd-admin as administration tool set. Mail hosting was done on a separate dedicated mail server. The error message reported by the client was theĀ infamous 550 sorry, user unknown Checking […]

Resolving IPv6 issues with GMail using qmail smtp

In case you are running into problems with Google Mail (GMail) rejecting mail from your qmail server running on native IPv6 with the following message 2a00:1450:4013:0c01:0000:0000:0000:001a failed after I sent the message. Remote host said: 550-5.7.1 [xxx:xxx:xxx:xxx::x 12] Our system has detected that this 550-5.7.1 message is likely unsolicited mail. To reduce the amount of […]