Why can't I post a message to the List sometimes?

Is Auto-Complete the culprit?

Many email programs include the Auto-Complete feature. This feature automatically lists names and email addresses when you begin typing in the To: or Cc: fields. The list populates from either your address book and/or people you emailed previously. It's a great time-saving feature, since you can quickly select the name, hit Enter, and the information is added.

Sometimes, the wrong email address is selected by accident.

Example

Let's say both of these email addresses are in my address book.

Enews@mail-list.com
Enews-on@mail-list.com

If I want to send a message to the list Enews, I need to use the first address listed. The second address is what I used to originally subscribe to the list.

When I start to type Enews in the email To: field, the system displays both addresses. I may select the second address inadvertently. In that case, my message to the list Enews will not be distributed.

How can I prevent this from happening?

Some software programs allow you to delete selections from the Auto-Complete list. See links below for help:

Microsoft - Manage suggested recipients in the To, Cc, and Bcc boxes with Auto-Complete
Gmail - Change who's saved & suggested as contacts
Mac Mail - Delete an Address From Mac Mail's Auto-Complete List

Make it a habit to always do a quick double-check and confirm messages are sent to the correct email address before hitting the Send button.