Error 451 - too many recipients

[#1]

I am repeatedly getting this error message (451) that there are too many recipients when sending emails from the webmail server.

With some emails addresses, it occurs with a single recipient.  In another instance, there were only about 5 recipients and I was simply replying (to all) to a previous email I had sent.

Can this be fixed?  It stops me from using the service.

[#2]

Obtain an e mail programme.

[#3]

Hi there,

I'm really sorry to see this. Are you able to try sending emails through basic webmail Here?

Let me know how you get on.

[#4]

I use the webmail because I have trouble downloading and sending emails through outlook when my computer connects over a VPN (using Zscaler).  I have no problem when I am connected directly to the network when I am at work. 

The webmail is a last resort as it is pretty useless.

[#5]

The problem is intermittent.  I will try this next time.

[#6]

I had the error again just now.  I was able to send an email through the basic webmail system.  However, the basic webmail system belongs in a museum not in the modern world!  Is that seriously PlusNet's fix!  

[#7]

Thanks for getting back to us @ACB77, are you able to PM me the setting you have in your client just so that I can review them?