you can now send attachments, html mail etc... your headers will be left alone.
can use a list of possible SMTP servers instead of a single one.
all configuration now grouped in a %mailcfg hash.
removes possible extra line-endings in headers.
e-mail address regex changes: . now accepts user@[xxx.xxx.xxx.xxx] . now refuses commas (they are only valid in quoted strings which $address_rx does not support). Comma separated recipients lists now work even with no space after the comma.
if you used an X-mailer header, the Mail::Sendmail vwersion was appended. It isn't any more.