501 Invalid Address error

Problem Description

When trying to send an email message with AspEmail, the following error is generated by the Send method:

Persits.MailSender.4 (0x800A0006)
501 5.5.4 Invalid Address

Other variations of this error for different SMTP implementations include:

501 Syntax Error

501 Invalid Address

501 malformed address

501 unacceptable mail address

553 malformed address

Solution

The most common reason for this error is failure to assign a valid email address to the mandatory From property:

Mail.From = "name@domain.com"

This error may also occur if a name instead of email address is specified for this property.

Another reason is invalid syntax in an email address passed to any of the methods AddAddress, AddCC, AddBcc and AddReplyTo.