Member Avatar for Thong_Ispector

I have had a real problem with Emails failing to send if they include an attachment

I can receive email with or without attachments and I can send email without attachments.

I am narrowing down the problem.

It is not the ISP

It is not XP

It is somewhere in Eudora or Firefox...

I am downloading a new copy of Firefox and Thunderbird (Email Reader)

Has anyone had a similar problem?

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  • Latest Post Latest Post by Real-tiner

Dani AI

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A short, focused follow‑up that expands on the existing replies from , and and gives concrete isolation steps and what to look for.

Most likely this is not a Firefox/Thunderbird bug by itself but something on that PC that intercepts or alters outgoing mail (antivirus/mail‑relay/firewall or a local SMTP proxy). That pattern — attachments OK from another machine or from webmail/IE but failing from the mail clients on one PC — is classic for a local filter corrupting MIME/base64 data or causing the SMTP transaction to be cut off.

Quick isolation checklist (run these in order):

  • Temporarily disable any AV/anti‑spam email scanning and any local mail‑relay service, then send a very small text attachment.
  • From the same PC, send the same file via webmail (Yahoo/Hotmail/etc.) to verify whether the network path accepts attachments.
  • Try a tiny file, a zipped file and the same file renamed to .txt to rule out size/type blocking.
  • Switch the client to use the ISP’s SMTP on port 587 (with authentication/TLS) or another known SMTP server to see if the problem follows the server.
  • Enable the mail client’s SMTP/connection logging and capture the server responses (look for 4xx/5xx SMTP errors or “connection closed” messages).

Why that helps: attachments are sent as MIME with base64 encoding; if a scanner or proxy modifies the stream (wrong line wrapping, injected headers, truncated data), the attachment is ruined. Check for a local SMTP proxy (netstat can show a process listening on port 25), check your AV product’s “email protection” or “smart mail” module, and inspect the SMTP log for rejection codes (450/550/554, “connection closed by peer”, etc.). If a system filter is found, disable the mail scan or reconfigure it — removing the local proxy or switching to direct authenticated TLS on port 587 usually resolves the issue.

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Member Avatar for DMR

Hey T_I,

Do you have an anti-virus program doing email checking? If so, turn that option off. Since you said the problem is not confined to one particular program, I'd start there first.

Member Avatar for DMR

By the way- I've deleted your earlier post on the matter, as it was essentially the same as this post and hadn't gotten any responses.

Member Avatar for Thong_Ispector

I looked and did not find the old one so I reposted..

I had updated info to try and narrow down the problem

The new Thunderbird and Firefox did not help.

IE can send files with attachments and I will try (Argh) Outlook to see if it will send email with attachments.

Why would IE work and not Firefox ?

I has to be something with Mime I would think.

Does IE have Mime built in it and my Mime is corrupt in XP?
Can I reinstall Mime? How?

I checked with my laptop and Firefox works fine with Yahoo...

This is just Odd..

Member Avatar for Real-tiner

I'd say that, if it is an attachment block, it is one of two places:

1. Outlook security settings

2. Your ISP (often they won't tell you about security measures implemented to stop attacks against the ISP itself).

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If it is not an attachment block, it could be:

A. The sender's ISP, especially if it is AOL.

B. Your ISP blocking the sender's ISP.

C. Failure of the sender to attach the file correctly (such as trying to embed some kinds files, rather than trying to attach them).

D. The attachment is larger than your ISP allows an email to be.

E. Spam or spyware filter blocking the email.

F. Virus checker detecting a virus.

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