Plusnet webmail

[#1]

Whenever I access my webmail whilst abroad and try to send an email, I am told 'error 501' syntax........
and unable to reply or send emails.
Can anyone help please? 

[#2]

Do you not get the same error if you access webmail in this country?
I suggest logging into webmail and selecting Options then Personal Information.
Make sure your Full Name and E-Mail address are entered properly.
The Reply To field should be empty (unless you want this to be different from your sender address on the previous line).
Click the Submit button at the bottom of the page if you change anything.

[#3]

Hi SPRAXYT
It only happens when I log into my webmail whilst abroad.
I am receiving emails but unable to send-even by simply hitting reply button.
Technical support have tried my webmail in UK-but cannot duplicate the error.
Any help much appreciated.

[#4]

Do you use the same computer (eg your own laptop) and browser when accessing webmail in this country and when abroad?