SMTP/SMTPauth/contact us conundrum

I can flip-flop between two errors but not avoid both:

1 - if using SMTP I can get the "contact us" page working fine, but there's errors in the ordering process in that relaying emails is refused "554 5.7.1 : Relay access denied". Customers don't know if their orders were successful and so forth. The log file says :

[05-Mar-2014 13:43:57] PHP Warning: Cannot modify header information - headers already sent by (output started at /home///includes/classes/class.smtp.php:1049) in /home///alternative admin name/includes/functions/general.php on line 21

2 - switching to SMTPauth the "contact us" page fails - "Email Error: SMTP Error: The following recipients failed: [email protected]" which is the store-owners email address. However, ordering is absolutely fine. No log error generated. Email archive shows the email was sent. Can send email from admin>tools>send email but returns a page of SMTP dialogue.

I've tried the "email_test_tool.php" and this is happy with SMTPauth but "relay denied" on SMTP.

The host is domainmonster.

Site is https://www.allwarm.co.uk

zc version is 1.5.1 - no upgrades

Template is Anne's Picaflor Azul: Stirling Grand

Thanks

It's something between the confessional and going to the dentist. Get it out in the open and it's mainly sorted.

I had Email friendly errors set to "false" in admin>email options . I think I am back in the game now. Sorry to disturb and hope this trail is informative for someone in the future.

No .. not sorted!

Using SMTPauth: Contact us emails not getting through even though Email-friendly errors is 'true'. They are in the archive and no SMTP debate on the screen but not getting through.

Question: When did all these symptoms suddenly start occurring? What did you change just before it started being a problem?

As far as I remember nothing changed just before. This is a new site so it was discovered in routine testing for web-worthyness.

I guess I'm really none the wiser but I have gotten this working. Working with the techies at DomainMonster we changed the address in admin > Email options > Set "Contact Us' email dropdown to another email address which worked and then back again and this time it worked on the contact us page but not the mega menu quick contact form. So I've commented out that part of tpl_mega_menu.php so "contact" isn't in the navigation/menu ... and things seem to function now. Grateful but unenlightened ....

Sounds very much like something amuck in their server email-handling rules.
Zen Cart is just the messenger, and hands off the envelope by sticking it in the post. Anything that rejects that attempt or fails to follow thru with delivery happens at a point after Zen Cart is done with its job in the equation.
Hopefully whatever your host changed will stick.