Help me understand FDQN as some of my mails are bouncing back


I am new to owning the VPS and learning alot of things, i search for for the answers on DO and came across alot of posts some made few sense and some none probably due to my lack of knowledge.

The problem I am having is after moving to DO some of my emails that I send are getting bounced back and the error I get it as following

(reason: 550 Access denied - Invalid HELO name (See RFC2821

After googling some posts suggests I need to look into my configuration to make sure they are done right for example make sure FDQN is setup.

When I run the command hostname i see my hosting listed on terminal so i am assuming that right, when i run the command hostname -f i see the following on terminal


So here is my first question is that right? is localhost.localdomain what we are supposed to be using? if not then how do i fix it and what to i change that to?

inside my host file i see the following lines localhost.localdomain hostname hostname localhost

Is this setup right? what am i missing?

Any help will be really appreciated


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i installed a mail server through this service from solvehostbd


The issue you are facing is that the initial response from your server to the sending server is based in the HELO command. This command allows you to identify yourself before sending email, and should contain your fully qualified hostname.

If the fully qualified domain name is not used, many mail servers will begin rejecting the mail as the server is technically misconfigured. For more information, please visit: and scroll down to section Extended HELLO (EHLO) or HELLO (HELO)

These commands are used to identify the SMTP client to the SMTP server. The argument field contains the fully-qualified domain name of the SMTP client if one is available.

Please let us know if there is anything else we can help you with.

Best, Mike