This image of the subject email would not attache in the message above.. re-attaching for clarity of issue

That error of sending message suggests it is from the godaddy server, but it is possible it is from another receiving server of one of the recipients. Thunderbird does not have a server.

If one of the recipients has a valid email address but it is either no longer used and has filled up with spam or their account has reached it's quota, that might cause the error message.

It might also mean the allocated temporary cache space for SMTP server has reached a max.

The error message seems to imply it is talking about the actual message size. The image says Thunderbird has blocked remote content so this suggests there is at least one image involved. There is no information regarding the actual size of the email because the 'Size' column header is not enabled. The subject length does not look too lengthy. The scroll bar on the left implies the email is only showing one third of it's actual content. So it is unknown what is in the other two thirds.

GoDaddy have a variety of limits, so I'm very supprised the help from GoDaddy did not offer some helpful advice.

Not sure what type of account you have but.....

Office 365 from GoDaddy

• https://uk.godaddy.com/help/check-the-limitations-of-my-email-9003

Quote: For your reference, here are the limitations that apply to Office 365 from GoDaddy email accounts:

• Message Size — 25 MB per message, includes message header, body, and attachments
• Message Subject Length — 255 characters
• Message Rate (Incoming & Outgoing) — 30 messages per minute, 10,000 messages per 24 hours
• Recipients — 500 recipients per message
• Shared Contacts — 1000 shared contacts
• Attachment Size — 125 attachments per message, not exceeding the 25 MB message size limit

• Note: OWA has a maximum individual file attachment size of 10 MB.

Workspace email https://uk.godaddy.com/help/email-account-limitations-2949 * Outgoing Mail Size (SMTP Relay) — There is a 30MB limit per email message that you send using SMTP, including file attachments, which have a size limit of 20MB total. Messages larger than 30MB are rejected by our outgoing server and you are notified. * Note: The receiving mail server may have different size restrictions. Many mail providers and ISPs will reject mail larger than 5-10 MB. * SMTP relays — SMTP relays let you send emails through our servers using third-party clients, such as Microsoft Outlook®. To prevent spam, we limit our email accounts to 250 SMTP relays per day. This lets you send 250 emails from your email address on a daily basis.

• Sent Mail Messages — To prevent spam, we limit the number of email recipients to whom you can send messages to 500 per day. There is a 200 per minute sending limitation as well as a 300 per hour sending limitation. Any distribution lists are expanded to their actual recipient lists and any duplicate addresses in a single email are removed. For additional information, please contact customer support.
• Outgoing Mail Size — There is a 30MB size limit per email message, which includes file attachments. Meaning, your message cannot exceed 30MB in size, including the size of your file attachments. File attachments have a size limit of 20MB total.
• Number of Addresses — There is a limit of 100 addresses on a single email message. The 100 addresses may be included in any combination of the To, CC, and BCC fields. If there are more than 100 total addresses, the Compose window shows an error and the message is not sent. You must revise the recipient list and then resend your message.

Thank you.. I will investigate .. no attachments, only text with a link to an application.

I have an unlimited email account with GoDaddy. I can send up to about 25MB of attachments per email. I have unlimited email storage.. it is a business account.

The issue is I can send out over Gmail and I actually sent it to GoDaddy on the 3rd try for their review. They were trying to fix something on their end while telling me it was a Thunderbird program problem. They had me on hold for about 15 mins.. and were still working on it when I told them I had to terminate the phone call and get back to my projects. They were suggesting I upgrade (buy) their new office 365 service. (it might fix it. they said). But wanted to stay on the phone with me while they continued to research the problem (would seem given that it was a problem on their end). I may just change email servers. I do not / will not use Microsoft. If I didn't have one business program that must run on Windows, I would be on Linux... I will review all your notes and see if I can determine whether the issue lies in the areas you have suggested. Thanks again. Bob

The use of the folder name "bulk mail" on your image would indicate yahoo are somehow involved. They are the only provider I have ever heard of that use that folder name. Everyone else used some variation on SPAM and JUNK.

If GoDaddy are subcontracting their mail through yahoo, prayer may be the only hope. Yahoo are known for many things. Answer's and responsiveness are not among them