553 - Unable to Send Mail / SMTP Auth (Mac)

Issue:

I can't send mail. The error message always begins with 553, followed by text similar to "Due to an error, you are unable to send mail".

Solution:

A sending error message that begins with 553 usually involves authentication being required. If you are having trouble sending mail due to an error regarding authentication being required, it is possible that your ISP is now requiring you to authenticate before you can send email. Authentication can be done in a variety of ways, the most common being "login" and "plain". Unfortunately, many mail servers advertise that they support the "plain" version, but do not do so correctly.

This plugin will solve this problem by causing Mac Eudora to use the "login" variety, even when the server advertises that it supports plain. To install this plugin, do the following:

First, in Eudora, select Special->Settings, then scroll to the "Sending Mail" panel and make sure that "Allow Authorization" is checked. If this alone does not fix the problem, do the following:

1. Download the file FixBustedSMTPAuth.hqx. It is a Binhexed Stuffit archive.

2. Unstuff the file with Stuffit Expander or similar utility. The resulting file will be called FixBustedSMTPAuth.

3. Move the UNSTUFFED file into your "Eudora Stuff" folder. This folder should be inside your Eudora Application folder (the folder where your Eudora application is installed).

4. Quit and restart Eudora.

5. In Eudora, select Special->Settings, then scroll to the "Sending Mail" panel and make sure that "Allow Authorization" is checked.

You should now be asked for your password when you send mail, and mail should be sent without error. If you STILL get an error sending, you may need to change the way your username is entered into Eudora. While the username is usually the part of your email address preceding the "@" sign, you may need to enter your full email address here. For example:

For user john_doe@somedomain.com
Typical: username = john_doe
Alternate: username = john_doe@somedomain.com

Be sure to ask your ISP which of the above you should use.

What is wrong with the way Eudora has implemented SMTP AUTH PLAIN? Nothing. We are in full compliance with RFC 2552. The important bit is the line in Section 4 of RFC 2552 that says "The optional initial-response argument to the AUTH command is used...". Emphasis on the word "optional". The problem we are seeing with some smtp servers out there is that they are REQUIRING the OPTIONAL initial-response argument.

The plugin will cause Eudora to ignore the server's support for AUTH PLAIN and will instead use AUTH LOGIN (if supported by the server) to authenticate.

KEYWORDS: EPMAC, SEND, SMTP, AUTH, AUTHORIZATION, ROGERS, EARTHLINK, ATT, AT&T