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Server Error: 421 EHLO MXIN201 - Error message for specific domains
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Cottonshope  
#1 Posted : Sunday, June 18, 2023 11:34:38 PM(UTC)
Cottonshope

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Hello!

I am using the EASendMail Service Manager on my server running IIS. There is a specific email domain that appears to be causing the error below whenever an email is sent to that domain:

SERVER_ERROR: 421 EHLO MXIN201 Your HELO/EHLO [REDACTED_1] is not matching your DNS configuration [REDACTED_2]


I can see within the EASendMail Service Manager that there is a field named "HELO Domain" - currently this is empty.

To clarify, I have hundreds of thousands of emails being sent successfully, it appears to just be 1 email domain that is having the error.

I don't typically handle the configuration of the EASendMail configuration, so I'm not sure what I might need to do to resolve this, as such is anyone able to offer any advice on how I should approach this?

Thanks!
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ivan  
#2 Posted : Wednesday, June 21, 2023 3:35:01 PM(UTC)
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Hi, you should set a valid internet domain whose A record is resolved to your current server IP address, then it should work.

for example, your current server IP address is: 192.168.xxx.xxx, your helo domain is mail.mydomain, then you should set a A record in your DNS server:

The record host is mail.mydomain, the record value is the IP address of your server.
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Cottonshope on 6/27/2023(UTC)
Cottonshope  
#3 Posted : Friday, June 23, 2023 12:44:30 AM(UTC)
Cottonshope

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Originally Posted by: ivan Go to Quoted Post
Hi, you should set a valid internet domain whose A record is resolved to your current server IP address, then it should work.

for example, your current server IP address is: 192.168.xxx.xxx, your helo domain is mail.mydomain, then you should set a A record in your DNS server:

The record host is mail.mydomain, the record value is the IP address of your server.


Hi Ivan,

Thanks for the response, when performing a DNS lookup of the A record, it does appear to have a value for the name, for example:

- example.server.net

Whereas the error message suggests that the HELO/EHLO is:

- example.domain

To resolve this without changing my DNS, would I be expected to populate the "HELO Domain" part of the EASendMail Service Manager with the value from my A record, so in this case "example.server.net" ?
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ivan  
#4 Posted : Friday, June 23, 2023 8:00:07 PM(UTC)
ivan

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you can set Helo domain in EASendMail Service Manager -> SMTP configuration.

If you specify the server in your codes, you can use Server.HeloDomain property to specify the domain.
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Cottonshope on 6/27/2023(UTC)
Cottonshope  
#5 Posted : Monday, June 26, 2023 7:55:28 AM(UTC)
Cottonshope

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Originally Posted by: ivan Go to Quoted Post
you can set Helo domain in EASendMail Service Manager -> SMTP configuration.

If you specify the server in your codes, you can use Server.HeloDomain property to specify the domain.


Thanks! I can confirm setting the HELO domain within the EASendMail Service Manager has resolved the issue for the problematic emails in the queue.

Regarding specifying the server within my code - currently I do not do this and the EASendMail.SmtpServer is declared as NULL. However I do have some emails that are sent immediately (SendEmail) as opposed to being added to the queue (SendMailToQueue). In this case, does the configuration in the EASendMail Service Manager affect those emails that are sent immediately and not via the queue?

I'm trying to identify if I'll need to update my code by specifying the EASendMail.SmtpServer details for these immediately sent emails.
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ivan  
#6 Posted : Monday, June 26, 2023 10:38:48 PM(UTC)
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If you specify the NULL to server and you always use SendMailToQueue method, then you don't have to change your code.

If you use SendMail method, you can do it like this (c#):

Code:

SmtpServer server = new SmtpServer("");
server.HeloDomain = "yourdomain";

oSmtp.SendMail(server, mail);

Edited by user Monday, June 26, 2023 10:40:52 PM(UTC)  | Reason: Not specified
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thanks 1 user thanked ivan for this useful post.
Cottonshope on 6/27/2023(UTC)
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