Thunderbird ont sending emails with PDF

I cannot send any PDF files regardless of size. The problem has developed over the last few days and now the Error message appears; "Sending of the message failed. The message could not be sent because the connection to Outgoing server (SMTP) mail.ivdc.co.uk timed out. Try again." When I try to save the email to drafts the error message appears; "Your draft message was not copied to your drafts folder (Drafts) due to network or file access errors. You can retry or save the draft locally to Local Folders/Drafts - acreceivable@ivdc.co.uk." It cannot save locally to this folder. I have verified the SMTP server and nothing is visibly wrong. This has been a progressive problem over the last two days with emails being slower with PDFs attached. I can still send emails without PDFs attached. I have the most updated version of Adobe Acrobat and Thunderbird.