Invalid HELO command ?

Problem reported by Merle Wait - 1/26/2022 at 10:50 AM

Resolved

We have had this outbound server / SM for quite some time....
But recently.. we are seeing more of these errors.... which cause the email to automatically be rejected back to our sending client's email.
Not sure what we have.. that has changed... Any ideas or suggestions would be welcomed....

[2022.01.26] 11:29:58.144 [71094411] RSP: 250-8BITMIME

[2022.01.26] 11:29:58.144 [71094411] RSP: 250-PIPELINING

[2022.01.26] 11:29:58.144 [71094411] RSP: 250-PIPE_CONNECT

[2022.01.26] 11:29:58.144 [71094411] RSP: 250-AUTH PLAIN LOGIN

[2022.01.26] 11:29:58.144 [71094411] RSP: 250-STARTTLS

[2022.01.26] 11:29:58.144 [71094411] RSP: 250 HELP

[2022.01.26] 11:29:58.144 [71094411] CMD: STARTTLS

[2022.01.26] 11:29:58.205 [71094411] RSP: 220 TLS go ahead

[2022.01.26] 11:29:58.328 [71094411] CMD: EHLO C5_gateway_out

[2022.01.26] 11:29:58.389 [71094411] RSP: 250-gator3044.hostgator.com Hello gate.XXX.net [XX.XX.193.231]

[2022.01.26] 11:29:58.389 [71094411] RSP: 250-SIZE 52428800

[2022.01.26] 11:29:58.389 [71094411] RSP: 250-8BITMIME

[2022.01.26] 11:29:58.389 [71094411] RSP: 250-PIPELINING

[2022.01.26] 11:29:58.389 [71094411] RSP: 250-PIPE_CONNECT

[2022.01.26] 11:29:58.389 [71094411] RSP: 250-AUTH PLAIN LOGIN

[2022.01.26] 11:29:58.389 [71094411] RSP: 250 HELP

[2022.01.26] 11:29:58.389 [71094411] CMD: MAIL FROM:<zzSendr@sendingDomain.com> SIZE=7623

[2022.01.26] 11:29:58.451 [71094411] RSP: 550 Access denied - Invalid HELO name (See RFC2821 4.1.1.1)

[2022.01.26] 11:29:58.451 [71094411] CMD: QUIT

[2022.01.26] 11:30:03.481 [71094411] Attempt to ip, '192.232.218.94' success: 'True'

[2022.01.26] 11:30:03.481 [71094411] Delivery for zzSendr@sendingDomain.com to john@ReceivingDomain.com has bounced. Reason: Remote host said: 550 Access denied - Invalid HELO name (See RFC2821 4.1.1.1)

[2022.01.26] 11:30:03.483 [71094411] DSN email written to 71094412 with status failed to john@ReceivingDomain.com

[2022.01.26] 11:30:03.483 [71094411] Delivery for zzSendr@sendingDomain.com to vijay@ReceivingDomain.com has bounced. Reason: Remote host said: 550 Access denied - Invalid HELO name (See RFC2821 4.1.1.1)

[2022.01.26] 11:30:03.484 [71094411] DSN email written to 71094413 with status failed to vijay@ReceivingDomain.com

[2022.01.26] 11:30:03.484 [71094411] Delivery for zzSendr@sendingDomain.com to vigneshs@ReceivingDomain.com has bounced. Reason: Remote host said: 550 Access denied - Invalid HELO name (See RFC2821 4.1.1.1)

[2022.01.26] 11:30:03.485 [71094411] DSN email written to 71094414 with status failed to vigneshs@ReceivingDomain.com

[2022.01.26] 11:30:03.486 [71094411] Process delivery status notification step from recipient success. Recipient: [john@ReceivingDomain.com], Notify: [failure], LastError: [550 Access denied - Invalid HELO name (See RFC2821 4.1.1.1)], RanDomainFilter: [False], RanGlobalFilter: False

[2022.01.26] 11:30:03.486 [71094411] Delivery for zzSendr@sendingDomain.com to john@ReceivingDomain.com has completed (Bounced)

[2022.01.26] 11:30:03.486 [71094411] Process delivery status notification step from recipient success. Recipient: [vijay@ReceivingDomain.com], Notify: [failure], LastError: [550 Access denied - Invalid HELO name (See RFC2821 4.1.1.1)], RanDomainFilter: [False], RanGlobalFilter: False

[2022.01.26] 11:30:03.486 [71094411] Delivery for zzSendr@sendingDomain.com to vijay@ReceivingDomain.com has completed (Bounced)

[2022.01.26] 11:30:03.486 [71094411] Process delivery status notification step from recipient success. Recipient: [vigneshs@ReceivingDomain.com], Notify: [failure], LastError: [550 Access denied - Invalid HELO name (See RFC2821 4.1.1.1)], RanDomainFilter: [False], RanGlobalFilter: False

[2022.01.26] 11:30:03.486 [71094411] Delivery for zzSendr@sendingDomain.com to vigneshs@ReceivingDomain.com has completed (Bounced)

4 Replies

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Kyle Kerst Replied

1/26/2022 at 10:51 AM

Employee Post Marked As Resolution

This error usually means they are rejecting the incoming message because your server isn't identifying itself with a fully qualified domain name that they can perform lookups on. To correct that you can adjust the Hostname fields found in Settings>Protocols and in the domain settings when logged on as a system administrator. I hope that helps!

Kyle Kerst IT Coordinator SmarterTools Inc. www.smartertools.com

Sébastien Riccio Replied

1/26/2022 at 11:06 AM

Yes, as pointed out by Kyle, your server is not announcing a FQDN hostname and many servers will reject this.

From your log:

[2022.01.26] 11:29:58.328 [71094411] CMD: EHLO C5_gateway_out

It should look something like c5-gateway-out.yourdomain.com

Also to avoid further issues your server public IP address should reverse resolve to the hostname announced in the HELO and the announced hostname should resolve to the server public IP Address:

Forward and reverse DNS must match
Also called Forward Confirmed Reverse DNS, having valid and matching forward and reverse DNS is one of the first recommendations in RFC 1912 ("Make sure your PTR and A records match"). It's a sign that the system administrator understands at least the basic RFCs, and it also helps to avoid spoofing by spammers.
HELO string must match reverse DNS
When an SMTP server sends email, it has to announce its name in the HELO or EHLO command. If DNS is set up correctly with fully-qualified domain name (the reverse DNS name), the sender can follow RFC 2821) and use it as their HELO/EHLO string:

Sébastien Riccio System & Network Admin https://swisscenter.com

Merle Wait Replied

1/26/2022 at 11:16 AM

Yep.. not sure how.. but it must have been "me" ...(uggghhh) ... put the server ID in, instead of the host name... for outgoing (under the port bindings).....

I did look at the hostname on general settings...

Must have Pasted inadvertently .. Now fixed.. and working

Thank you so much for the speedy response...

Kyle Kerst Replied

1/26/2022 at 4:56 PM

Employee Post

Good call including the RDNS details as well Sébastien! :) You are very welcome Merle, we're happy to lend a hand.

Kyle Kerst IT Coordinator SmarterTools Inc. www.smartertools.com

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