Troubleshooting email delivery for Postfix/CentOS

Troubleshooting email delivery for Postfix/CentOS


Job Description

I need to ensure that my emails are delivered on time.

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 10-50 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,, etc.

I receive 20-100 emails per day that the emails I am trying to send 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
- 550 5.1.1 unnecessary spaces. Learn more at 550 5.1.1 bk8si48484441wjb.30 (in reply to RCPT TO command)
- etc

I get this for various mail servers including gmail, yahoo,, 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[] said: 451 (in reply to RCPT TO command)

The link goes to the page on that server where they suggest "to properly setup queue runners". Well, to my knowledge PostFix does have message queues.

3. Unauthorised requests

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

What I need is to make sure that my emails are delivered to recipients.

Possible tasks:
1) Review rejection emails I receive: which one of them are real indication of problems?
2) Postfix configuration review: better security, better delivery rate, etc? Anything that may improve the delivery is welcomed.

Please apply if you can help me with that.

I assume that this is a more or less straightforward task for a professional. However, if you convince me that this job required more I may increase the budget.

Due to security policy I will not be able to provide you a root access so either you tell me what to do via Skype Share Screen or we do something similar.

Thank you.