Inability to send emails on 4G

[#1]

I use an iPhone SE2020. My mobile data is on but I cannot send emails on 4G. I get the response “server has rejected one of the recipient’s addresses”. This comes up regardlessof the recipient. Can anyone help?

[#2]

Are you using pn email or another service?

[#3]

Plusnet.

[#4]

Is your outgoing smtp server configured to authenticate with your Plusnet username and password ?

[#5]

Moderators Note

This topic has been moved from Mobile to Email

[#6]

Yes.

[#7]

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@Guide2015 wrote:
Yes.

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The problem with many email clients is that they don't give detailed error messages, rather just a 'failed to send

There are two common problems with sending via mobile networks

1) the need for authentication ad i previously said. You say you have authentication configured, so If sending via a plusnet wifi connection works then that isn't the problem

2) the 'reputation' of the ip address you are sending from. Mobile networks share or reallocated ip addresses and if the previous user of that ip has sent spam then the ip will be marked as poor. This  is usually a transient problem and the reputation improves within 24 hrs or so

[#8]

Many thanks but it has been a problem for several weeks, if not longer.

[#9]

In that case you need to find the exact error that is being returned by the smtp server. If the email client isnt returning the full error message , then using telnet as described in this thread https://community.plus.net/t5/Email/Cannot-send-emails-I-recieve-mails-ok/m-p/1758052 is one method. As to how to use telnet on an iPhone, Im afraid I dont use an iphone so we'll need someone mre familiar with Apple software.

[#10]

Many thanks - I think the problem is solved although I am not sure how!

[#11]

Invalid recipient is usually indicative of no attempt to sign on to the server.  Are you sure that you have not confused encryption with credentials?

As for the situation where you cannot sign on over 4G as mentioned by @MisterW due to IP addresses having a poor reputation, then you can test that on any device having a telnet client.  You can download one of those from the apple store and follow the referenced guide.  However, the need to generate copy and paste base64 encoded text is somewhat cumbersome on any touch screen device. 

It is possible that the iPhone got its settings screwed up such that it was not authenticating properly.