E-mail headers. Bounce back e-mail. SMTP relay. Unable to unable to relay 5.7.1.

Hi there

- Can someone please advise me on what are the information that can be most useful to analyse bounce back messages is it bounce back messages or the e-mail headers?

- Can someone please give me one good simple explanation on SMTP relay. (A good link will do)

- Many times I have seen this message: unable to relay 5.7.1 when users tried to send from applications. Can some one explain that to me simply and briefly.

M SOSAsked:
Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.


1. the information importent on bounce backs is the error number (i.e Unable to unable to relay 5.7.1)
    that can tell you where to check, look for the error code in google to get more info, in general that error means
    that the station or server that is used to sending mails is unable to relay (send email) smtp due to permissions issues   most of the time (the server used for sending/relay is not on the list of relay servers)

2. smtp relay is a connection that is using smtp (mail sending protocol) to send emails through that connection  that exists outside your mail server , this is called smtp relay because sometimes not the server itself is the sender by using the local smtp service, for example you have a server but you want to use smtp relay, you want the emails to go through that connection because it is filtered, secured, or on DMZ, examples are endless..
few years ago smtp relay was not a must, today with all the spam and regulation this is the best solution.
see here:

3. unable to relay 5.7.1 when users try to send means they have no permission to use this smtp relay/ or the sending server has no access permission to relay through this smtp connection. this is common and can be solved easily if you know the server configuration, what server are you using?
see this classic example on relay access list:

post back for more questions..
M SOSAuthor Commented:
Thank you very much

But still question no. 1 is not very clear

What is the difference between e-mail headers and bounce back messages, which is more descriptive of the problem?

In my opinion both are important   to understand the problem, you defiantly need the bounce message you don't need the email headers to describe the problem only in some cases when the bounce is related to the header (unknown email address, unknown domain) or you just need the message details, NDR (bounce backs) are generated by the server and will not return the email headers..

see here:

you welcome!
Big Business Goals? Which KPIs Will Help You

The most successful MSPs rely on metrics – known as key performance indicators (KPIs) – for making informed decisions that help their businesses thrive, rather than just survive. This eBook provides an overview of the most important KPIs used by top MSPs.

M SOSAuthor Commented:
But supposedly the e-mail header show all the way and the hops e-mail travelled over which provide more information than the bounce back message right?
correct, the path will always be the same unless your server stopped it - then you need the NDR message with the error code, otherwise you need to guess why the email bounced back..
M SOSAuthor Commented:
So both are important in case of a bounced back e-mails right?
yes, but most of the time the NDR is enough to troubleshoot mail delivery errors..

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today

From novice to tech pro — start learning today.