BulkMTA is described as 'is Commercial Mail Server Similar to PowerMTA' and is an app in the Online Services category. There are six alternatives to BulkMTA for Linux, Mac and Windows. The best alternative is Postfix, which is both free and Open Source. Other great apps like BulkMTA are Exim (Free, Open Source), sSMTP (Free, Open Source), Sendmail (Free, Open Source) and Microsoft SMTP Server (Paid).
Postfix is a mail transfer agent (MTA) that routes and delivers electronic mail. It attempts to be fast, easy to administer, and secure. The software is also known by its former names VMailer and IBM Secure Mailer.
sSMTP is a simple MTA to deliver mail from a computer to a mail server. sSMTP is simple and lightweight, there are no daemons or anything hogging up CPU; Just sSMTP. Unlike Exim4, sSMTP does not receive mail, expand aliases, or manage a queue.
Sendmail is a general purpose internetwork email routing facility that supports many kinds of transfer and delivery methods, including the Simple Mail Transfer Protocol (SMTP) used for email transport over the Internet.
Configure SMTP e-mail in IIS when you want to deliver e-mail messages from your site. Mail can be delivered immediately or it can be delivered to a file location on disk where it can be retrieved for delivery later.
NikaMail is a portable, extendable, zero-config email server. It is designed to perform automation tasks, provide access to mailboxes (port 110), serve as a mail transfer agent (port 587) and mail exchange service (port 25). NikaMail supports TLS.