By the way, ISPs will give all kinds of nonsense reasons for why they filter outgoing mail based on "from" header. The "security" reason is total bullsh*t. From a security standpoint, it is important to keep an association between the IP addresses where mail originates and human users. That way when spam or other malicious email is received, it can be traced back to a human and that human can be punished. ISPs have this association because they keep a log file of users logging in and which IP address they are assigned. So the accountability is maintained at the IP address level, not at the email address level. It shouldn't matter what is in the "from" header. Anyone who claims that it matters is either ignorant or deliberately misrepresenting the email security situation.