Is there a limit on e-mail attachments?

[#1]

I use the current version of Thunderbird as my e-mail client.
While I have several incoming mail accounts using other ISPs as well as PlusNet,  I only have one outgoing SMTP server, relay.plus.net, set up as default with authentication disabled.
I have generally have no problem forwarding e-mails: occasionally when I try to forward one with files attached the Delivering message progress bar starts, gets to some percentage then after  a pause the  "Sending of message failed: The message cannot be sent because connecting to SMTP server relay.plus.net failed" message is displayed.
I have just tried to forward a message with 5 .pdf  and 1 .doc file attached, and progress reaches 59% before failing.
Do PlusNet put a limit on the total size or number of attachments per message? Do I need to alter some parameters to get round this problem?

[#2]

There is no limit on the number of attachments and the attachment limit is 100MBytes.
How big are the attachments?

[#3]

Isn't that limit the total size of the email?
Also don't forget that attachments have to be 7-bit encoded. For example an email I received with a 8.5M zip file attached was 11.5M in the mailbox.

[#4]

Total size of 5 .pdf files 1.9 mb.
Size of 1 .doc file is 228 kb.

[#5]

Yes, the attachment figure I stated was the total for all attachments. Your attachments are well below that limit even allowing for 7bit encoding.
Try disabling any software firewall and A/V software temporarily as they can sometimes interfere with sending emails.
Also try zipping all the files into a single zip file and see if it sends then.

[#6]

This gets odder and odder:
I tried putting all 6 files into a zip archive and sending that - failed at 42%!
Next tried sending them separately - all were sent correctly except for 1 .pdf file - a map, about 900KB in size. This failed: I zipped it but also failed at about 42%! I shall now print it out and pass it manually.
Thank you for your help Peter: it's just a minor annoyance but I'd like to know why it failed. I've sometimes had similar problems forwarding full format .jpg files from digital cameras - I resize these to 800 x 600 which solves the problem. Also Thunderbird/PlusNet sometimes have problems forwarding attachments having very long file names - renaming with short names solves this one.

[#7]

I dont know where your problem lies, I happily sent 4 jpegs last night, total size 9.8 mb, vie OE which generally is not as good as thunderbird