Email errors are quite frustrating especially when you do not know why it is happening!

Though the bounce mail show some error text, that will just serve as a pointer to the possible reasons for the error.

One such error is “Destination smtp server rejected the sender” shown in email marketing programs like SendBlaster.

At Bobcares, we resolve many email related errors as part of our Outsourced Technical Support services for Web hosts.

Today, we’ll see the top reasons for this error and how we fix it.

What is “Destination SMTP server rejected the sender” error?

In any mail transaction, there is a sending server and a recipient. All mails do not reach the destination server. At the receiving side, there are many checks to prevent fraud mails. When this receiving server has a doubt on the authenticity of the mail sender, it reject mails from such servers.

And a bounce message in such cases will look like :

Your Incoming messages could not be delivered to your email ([my email]) because the Destination SMTP server rejected the sender.

Causes and Fixes for “Destination SMTP server rejected the sender” error

There can be many reasons for this error. We will have a close look at them.

1. SMTP settings

The “sender rejected error” mainly happens when the outgoing mail server (SMTP) settings are setup wrongly in the mail clients like Outlook, Windows Mail etc.

Typically, email users set the email port wrongly.

Solution

So, when user’s report this error, our Support Engineers ensure the correct mail server settings first. This include:

1. Correct mail server name
2. Email port – 465 or 587
3. Authentication type
4. Correct email address and password

We have also seen this error in Gmail. This happens when people use an account where google-apps is not configured.

Bulk mail sending programs like SendBlaster allows direct mail sending or mails via an SMTP server.  Certain e-mail domains, for instance, hotmail don’t allow direct sends. Then the message gets rejected if it originates from a desktop system as opposed to a public SMTP server. So to fix, we configure SMTP server details to send mails successfully.

2. Poor IP reputation

Another reason for email failure is bad reputation of the IP from which mail originates. The reputation of the IP can go bad when there are multiple spamming instances from an IP. Eventually, the IP is blacklisted at Spam monitoring tools like SORBS, DNSBL etc.

Solution

Here, to solve the problem and send mail, we need to ensure that the mail originating IP is clean. If at all it is blacklisted, we take corrective actions on the server and request a delist. Usually de-listing happens in a few days time.

3. Bad DNS

Similarly, mail block can occur due to the issues in the dns records of the domain. These DNS records helps destination server to cross-check that the sender is a genuine one.

To defend spam, mail servers typically checks the following values as part of dns check. The main records are:

1. SPF record

This record tells which all IP addresses can send mails on behalf of the domain. Often, when there is a change in mail server IP, the SPF record do not contain all the IP addresses from which mail originates. As a result, it may result in the error “Destination smtp server rejected the sender”.

2. DomainKeys Identified Mail (DKIM)

DKIM is a method to prevent email spoofing. It helps to associate a domain name with an email message by affixing a digital signature to it.  As a result, the mail server can confirm whether mail originates from the valid domain itself.

3. Reverse dns

Reverse DNS is the name that matches to IP address of the server. For mails to work, the forward and reverse dns should match. That is, if a server xyz.mailserver.com points to the IP address 192.168.x.34, the reverse dns of IP should be xyz.mailserver.com

Solution

When an error pops up, our Support Engineers verify the SPF, DKIM records of the domain. When there is a mismatch, we correct it by making enough changes in the dns records.

Conclusion

The error “Destination SMTP server rejected the sender” can happen mainly due to reasons such as bad mail client settings, wrong dns settings of the domain etc. Today, we have seen the top 3 reasons for the error and how our Support Engineers fix them.