MacMail crashing after sending email

[#1]

Soon after my migration to Greenby my iMap folders disappeared.  To get them back I deleted and re-created my plusnet account in my Mac client.  This resolved the folder problem but since then I've had problems sending outbound emails.

Initially the messages (even to myself)  just disappeared then the Mac mail client started to crash a few seconds after trying to send.

I again deleted and re-created my plusnet account in my client and sent a number of test messages.  For the first 5 messages everything was fine, but for any further messages the client has crashed.   

i accept that this might be a client side problem, but it's strange that these problems have only started since migration....no problems prior to that.  

Is anyone else seeing similar problems?

for the record I'm running macOS Ventura 13.7.8 on a MacBookAir with an M2 processor.    in the absence of other ideas I'll probably upgrade macOS, but that's quite big leap so I'm being cautious.

[#2]

@chalkridge 

What settings for server name, port, encryption and authentication do you have now?

Are you sure they are what you had previously?

[#3]

I'm currently running with

   Hostname:  relay.plus.net

   Port:  587

   Authentication:  Password

   Use TLS/SSL checked.

I've tried  other settings as recommended in various forum posts but they still didn't allow outbound mail to be sent.  

[#4]

SMTP Port 465 is used with SSL/TLS encryption

OR

SMTP Port 587 is used with STARTTLS encryption

If the email client is still unable to send, try a test send from webmail : webmail.greenby.com

[#5]

thanks for your suggestions.  I'm testing them now.

The client still crashes when using Port 465 with SSL/TLS

For Port 587, the Mac mail client I'm using doesn't appear have an option for STARTTLS.  What do you recommend?

I have send emails from Greenby Web mail.....even to hotmail addresses.

[#6]

Some online instructions say use TLS/SSL with Port 587.     I have tried that with Authentication set to password, but the cilent still crashes.

[#7]

Are you using the correct SMTP server :

https://greenby.com/support/knowledgebase/article/29

[#8]

@PhilipHeyes those  ports look horribly outdated/wrong to me.

[#9]

What can I say ... I did mention this legacy port issue as bad guidance only a few hours ago !

[#10]

@chalkridge is macmail failing when sending the message or when trying to store the message in the sent folder ?

[#11]

I have tested the settings recommended in the article.  

Of the 7 test messages I have sent 3 have succeeded and 4 have crashed the client.

Strangely replies to an existing message don't crash the client. 

[#12]

It's hard to say exactly....the message don't get sent or added to the sent folder.   I assume that the send operation is done first so i'd say it's the send that causes the client crash.

[#13]

That's my theory out the window then....

[#14]

Update:

I have stopped the mail client from crashing by changing the Undo Send Delay to 20 secs. 

So now I'm just left with the original problem that outbound emails just disappear......not reaching the recipient nor in the Sent list and no non-delivery notifications in the Inbox or junk.

The Mac Mail Connection Doctor tool shows both connections are 

I have trawled the Apple community found a post from 2023 which describes a very similar problem.

https://discussions.apple.com/thread/255154654?login=true&sortBy=rank

The summary of that thread is that the crashes are possibly server side problem that the client doesn't handle it properly when Send Delay is off.  

But i'm still no wiser about why outbound emails are failing.

  Is there any further logging I can enable to see what's happening?

[#15]

I managed to use the Connection Doctor logging to track an outbound message.

The final log file entry is:

READ Mar 12 20:44:28.586 [kCFStreamSocketSecurityLevelNone] -- host:relay.plus.net -- port:25 -- socket:0x6000003773c0 -- thread:0x60000396f080
250 0mtPwOm2ukMb10mtQwy1iK mail accepted for delivery

The final line saying  "mail accepted for delivery". seems to imply that connection and submission is happening Ok, but the message isn't being handled by the relay.    

Anyone disagree with my conclusion?