Common error messages.

There is at least one BCC recipient invalid (Applies to those using the "BCC recipients" checkbox)

You have one or various invalid recipients. Strip it out manually, or go to the Preferences window and check "Validate recipients", then import your recipients again. If it finds invalid recipients, it will create a filtered list of valid email addresses, and will let you export a list of invalid or duplicates, so you can review them.

If you enter the addresses manually (eg, copy-paste), they will be checked when you hit the Start button, before the message is delivered, and you will have a chance to abort the operation (and see the list of invalid and duplicates).

There are two kinds of valid recipients:
- a@a.com,b@b.net
- "Foo Bar" <foo@bar.com>, "Bar Foo" <bar@foo.com>

If you use the second notation (name, email), deactivate the "Validate recipients" option, as it will mark them as invalid (it will only validate the first kind of recipients: plain email addresses without spaces).

Whatever happened while I was sending a message to lots of recipients and the operation was aborted. Who received the message, and who didn't? (Applies to those using the "BCC recipients" checkbox)

XMail (the mail engine) creates groups of 100 recipients. If the "Validate recipients" function didn't catch previously the malformed email address, it may be a really valid email address, but the SMTP server could mark it as invalid (eg, dead domain, etc.). Just locate the offending address in your list (eg, "foo@bar.net"). If it is the address number 717, the first seven groups of recipients should receive the message (addresses 1 thru 700). The operation is aborted in the eighty group. So, messages 700 thru the end won't receive the message.