Using Mozilla Thunderbird

[#1]

I use Mozilla Thunderbird as my e-mail client and with that I use 4 e-mail addresses. My main e-mail is thro Plusnet and the others thro gmail.com. All works fine and well. However just lately I am taking my laptop to my son in laws house and using his Virgin Media connection to access the internet and email. All my G mail accounts work as well as they did at my home address. Plusnet account receives e-mail but I cannot send them. I have accessed https://portal.plus.net/support/email/setup/thunderbird-smtp.shtml and set-up the account as shown there. I have re-booted the laptop several times but still cannot send.
Have you guys any suggestions?

[#2]

That should work ok AFAIK.
You could try port 587 instead of the normal 25. Some ISP's can block port 25 although I didn't think VM did!.
You could also try using a username of the form username+mailboxname and the mailbox password ( as used for Webmail ) since that is supported now.