451 4.2.0 internal queueing error

Can you post the entire error? I know error 452 is when you send more then 100 messages at one time or sent too many over a certain period of time, but that is only from Cox. First need to know what server is giving the error.

No solution here, but I've been getting the same error message -- although I'm using Firefox 50.1.0.

As you say, when I try to resend after clearing the error message, the email sends just fine. Just started yesterday, but still happening randomly today.

Yea, then it's probably their new servers failing if more then one person is having the same error. I knew Cox email was going to be bad when they outsourced. Just wait until you have to call a "special" number to get email support. Then it will truly be the end.

I feel so much better now.

An error occurred while sending mail. The mail server responded:  4.2.0 Internal queueing error. Please check the message and try again.

I get my error through Norton after sending the email - Norton picks it up as it comes back and displays it. BTW, I've tried inserting the image, etc but no luck with that. The entire error is simply as noted in the subject. All the rest of the info is the To, From, Subject of the email.

Disable Norton from scanning outbound. As long as you scan your inbound and your computer, you won't have any malware on your system that you have to worry about outbound. See here for instructions.

The reason I have seen it cause problems is Outlook will open the connection to the SMTP server and keep it idle as Norton scans it. The way Norton handles this can cause some SMTP servers to error out. My guess is something changed with Cox's SMTP server that exaggerated this effect.

I was thinking about it some more in researching another thread, and I wonder if changing the server timeout will help. My guess is since the server is now off Cox network, the time it takes to communicate with it is longer, and anything that slows it down can cause the problem.Stopping scanning will decrease the amount of idle time needed, but increasing the amount of time the client can go idle before error might help more. See here for instructions. 

I've been getting this message now every time I send email.  Also using Outlook (mine is Mac 2011).  When I then resend, it goes through fine.  Not sure how to fix.

I'm getting same error.  Just started on Monday, 1-13-17.  Called.  Told to shut computer off and turn back on...nope, didn't work.  What now?

Either try my work around yet? Also, can either of you confirm how many account are set up in your Outlook, and how many of them are for Cox? Last, does this happen on any other email client except Outlook?

On the Norton workaround, it may have although I just had it happen again - may have been that I didn't shut the outgoing scan off permanently, only to next reboot. Yes, I just rebooted and it happened.

Setting the timeout through Outlook to 5 minutes doesn't sound like it would work. Currently it is set at 1 minute and the issue comes back within 10-15 seconds after sending the email.

Have you tried the server time out? Even if the problem is Cox server is just taking longer to respond, setting the timer longer means it will try for longer before giving the error, so you don't have to resend. Basically increasing the time out increases the buffer time.

Server timeout is currently set to 1 minute. However, I don't think this is the problem as the error will come back within 15-20 seconds, if that long. So whatever it is, it is happening quickly. I've never had one error take longer than the 15-20 seconds. If I get passed that, the email has gone on.

Ok, then I go back to my default suggestion; Cox email now stinks and you should change email providers as soon as convenient. 

PS. Any regulars here want to use my Cox email address for testing? It is on the older servers, isn't effected by most of the reported problems on the new server, and isn't attached to any account info. Or does anyone have a test email that is effected I can test with?

Having the same issues started 1/20/2017 - never had the problem before.  The problem exists with replying and forwarding only at this point.  Using Mozilla email for years and cox for years as well.  As it just started something with Cox email servers must be the issue.