Unable to Send iCloud Mail - 554 5.7.1 Client host rejected: Access denied

I finally solved this myself. I had opened a ticket with Apple Support way back in January. Since then I'd spoken with three different senior support people; none of whom could solve it. All three of them eventually ghosted me and I never heard from them again.

The first hint was when the exact problem appeared for the first time yesterday on my Intel iMac. Same error message in the Connection Doctor log and same symptom of two iCloud servers in the Outgoing Mail accounts list.

Here's what I did:

• Go to Edit SMTP Server list and delete iCloud. Deleting the one there deleted both of them in the Outgoing Mail accounts list.
• Turn off iCloud Mail
• Reboot the machine
• Turn on iCloud Mail
• Send mail from my iCloud account. It will tell you that there is no Outgoing Mail server, but it will have created one that you can select.

Oddly, the iCloud server is shown in the Outgoing Mail server list, but not in the Edit SMTP server list.

This procedure worked on both the MBA and the old iMac.

This on a 15" M2 MBA running MacOS 14.4.

I've had difficult email problems with this machine ever since I got it. Now a new one has popped up. (Two Apple Support Senior Specialists simply ghosted me when they couldn't solve the previous TLS authentication errors.)

This new error appears as follows in the Connection Doctor log for smtp.mail.me.com:

READ Mar 26 04:50:47.891 [kCFStreamSocketSecurityLevelTLSv1_2] -- host:smtp.mail.me.com -- port:587 -- socket:0x60000803dbc0 -- thread:0x6000071109c0

554 5.7.1 <node-17t8.pool-101-51.dynamic.totinternet.net[101.51.221.nnn]>: Client host rejected: Access denied

Oddly, the list of outgoing mail servers includes two for iCloud. I can sometimes fix the error by picking the one that is not selected. (Sometimes neither is selected.) Sometimes that enables the outgoing mail; sometimes not. If I keep switching servers, it eventually works, usually.

This even happens when I'm sending an iCloud message to myself; iCloud to iCloud.

It appears that Apple's SMTP server periodically doesn't like the IP address from which I'm sending the mail. (I'm not really sure about that.) This is odd because I have a dynamic IP address assigned by the ISP. The ISP is NT, the National Telecommunications company of Thailand (formerly TOT, hence the totinternet domain in the log message).

However, this problem does not affect my iPhone or iPad or my wife's M1 iMac. That should put to rest any idea that the problem is IP address related.

I am anxious to solve this problem as it is kind of a pain in the rear to have to keep selecting an outgoing SMTP mail server every time I want to send mail.

If you have ideas, please post.

Please do not suggest that I contact Apple Support as they have proved to be somewhat useless in the past. (As a long time Apple shareholder this bothers me a lot. Sadly, not much I can do about it.)

Duplicate Post - By way of explanation

I tried to edit the original post but got a message saying something like, "We are unable to process your request."

So, instead of editing I decided to just add an additional line of explanation as a reply.

When I checked the post some time later I was surprised to see that both the original post and the edited version both appear as separate posts. Clearly, something wrong, but I don't know what it is.

However, this problem does not affect my iPhone or iPad or my wife's M1 iMac. That should put to rest any idea that the problem is IP address related.