The From: header field differs from the from parameter in nearly the same way as the To: header differs from the to parameter. The from parameter is a separate command to the SMTP server, and is used to identify the sender to the SMTP server, not necessarily to the recipient of the message. Typically, however, they are the same, with the possible addition of an informal text version of the sender’s name in the From: header (e.g. "Big Brother <bigbro@us.gov>" instead of just bgpro@us.gov"). SMTP servers will often insist that the from parameter specify a valid address (since it needs this if it has to return the message because it was undeliverable.) They may or may not put restrictions on the From: header, but apparently this is not too common or we would not be deluged with junk-email with no usable From: address. Note that since your From: header is likely to be the same for all messages, you may want to put it in the configuration file and not bother with it in each message.