I run a little greeting cards web-site on VPS. It uses Postfix to send greeting cards to clients. Currently the volume is tiny, about 10-20 cards per day. There is absolutely no spam activity (at least to my knowledge) and my IP is not blacklisted in such organizations as MAPS, www.abuse.net, etc.

I noticed that there are cases when the emails are not delivered. There are 3 major types of faults:

1. User mailbox rejections


  • 550 Message was not accepted -- invalid mailbox
  • Recipient address rejected: User unknown in relay recipient table (in reply to RCPT TO command)
  • The e-mail address you entered couldn't be found. Please check the recipient's e-mail address and try to resend the message. If the problem continues, please contact your helpdesk.
  • 550-5.1.1 The email account that you tried to reach does not exist. Please try 550-5.1.1 double-checking the recipient's email address for typos or 550-5.1.1 unnecessary spaces. Learn more at 550 5.1.1 http://support.google.com/mail/bin/answer.py?answer=6596 bk8si48484441wjb.30 (in reply to RCPT TO command)
  • etc

I get this for different mail servers including gmail, yahoo, mail.ru, etc. I admit that some users may make a typo but it appears that the rate is way too high, I cannot believe there so many typos can be made.

2. Greylisting

One server reports this:

host mxs.ukr.net[] said: 451 http://ukr.net/mta/std3.html?my_ip (in reply to RCPT TO command)

The link goes to the page on that server where they suggest "to properly setup queue runners".

3. Unauthorised requests

host mx9.i.ua[] said: 451 Unauthorised request. Try again later (in reply to RCPT TO command)

Here are my questions, applicable to my case:

  1. How difficult would be to fix these issues?
  2. Would you recommend to hire a professional IT-specialist to configure email server?

Any help is much appreciated.

  • 2
    if the rate of mistyped adresses to freemailers is unusually high I'd check your logs if spambots are trying to abuse your form. make sure you have captchas or similar anti-bot measures in place.
    – Gryphius
    Jan 4 '13 at 17:32
  • The thing is that I have 10 cards per day on average so I am not sure if spambot would do such tiny sending. Do you think it is possible?
    – Alex
    Jan 4 '13 at 17:37
  • Unless you have real users complaining that their cards are not being delivered, the generic answer to questions like this is, "Welcome to the Internet". Jan 5 '13 at 0:44

You can't really "fix" a user who mistypes an email address. So there's not much you can do about those bounces.

As for the two greylisting examples you gave, just wait them out; postfix will resend the messages.

  • Could the "mailbox not found" type messages be related to my side?
    – Alex
    Jan 4 '13 at 17:31
  • Only if you screwed up the email address, and not the user. Jan 4 '13 at 17:32
  • 1
    Right. Postfix will resend the message automatically, if it's running. Its queue runner is named qmgr and should be one of the processes running on your server. Jan 4 '13 at 17:36
  • 1
    The "Unauthorised request" is just another greylisting. Jan 4 '13 at 17:37
  • 1
    Yes, essentially, what you experience is normal and there isn't much you can or need to do about it.
    – daff
    Jan 4 '13 at 18:21

1. There may be mistyped addresses or your software writes them incorrect but it is unlikely a server problem.

2. and 3. Errors starting with 4** is not permanent and mail server should store such emails in queue and deliver later. This feature is exploited by graylisting, because most spammers send e-mails using scripts and do not implement queue. So it is a normal behavior, that mostly do not require fixing. First check, if those emails do not get delivered later.

More on 3. Error number is a real error reason. Text after it can sometimes be misleading. Better check, what specification says about error number.

  • Could you please tell me how to check if those emails had been eventually delivered?
    – Alex
    Jan 4 '13 at 18:10
  • 1
    Check your mail queue with the mailq command to see which messages are still held and review the Postfix log files (probably /var/log/mail.log) once the queue is empty. The logs will tell you if the messages were delivered properly or, if not, what happened to them.
    – daff
    Jan 4 '13 at 18:18

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