smtp-cli is an SMTP command line client with support for advanced features such as STARTTLS, SMTP-AUTH, or IPv6. It also has scriptable message composition capabilities supporting anything from simple plain-text messages right up to building complex HTML emails with alternative plain-text part, attachments, and inline images. It's also a convenient tool for testing and debugging SMTP servers' setups. smtp-cli can be used to check a given server's capabilities, to test your server's setup, or to create and dispatch email messages. The command line interface is intuitive, and everything is scriptable and can run in a completely non-interactive mode from scripts or cron jobs. smtp-cli is ideal for shipping log files from remote machines, running periodic mail delivery test loops, etc.
Proto Balance Mail is an enterprise SMTP cluster solution that supports distribution of email accounts. It scales up to 1,000,000 mailboxes apportioned over up to 125 backend mail servers (8000 mailboxes per server). No NFS or SAN is required. SOA is configurable with SOAP/XML. Anti-spam settings can be set per-user. Grey-listing is supported. Mal-ware is automatically detected and infected client PCs are automatically black-listed. POP load balancing is done. SMTP AUTH is supported. There is a Web-based management interface. Spam blocking is done by on-the-fly connection behavior analysis. It handles up to 10,000 concurrent SMTP connections. Streamlined CRM integration is done with HTTP+XML posts. Email-alias lists, forwarding, and out-of-office auto-reply are supported.
Melon MailServer is a simple mail server emulator for developers. It can emulate POP3 and SMTP services. The SMTP facility receives and stores all the messages sent to it rather than sending them. The POP3 facility allows you to download any messages without authorization. The server is designed to accept all messages for any email accounts. It can be very useful for testing Web applications and other software applications.
CleanMail is a complete SMTP/POP3 email security solution that fights against spam and viruses. It works with any mail server like Microsoft Exchange 2003/2007/2010, Microsoft Small Business Server (SBS) 2003/2008, Lotus Notes/Domino, or IMail. CleanMail includes a comprehensive set of filters, including an attachment blocker, remote blacklist filter (DNSBL), and a complete build of SpamAssassin.
libquickmail is a library intended to give C/C++ developers a quick and easy way to send email from their applications. It supports multiple To/Cc/Bcc recipients and multiple MIME attachments without size limitation. It uses libcurl for SMTP communication, but a light version is also included without the libcurl dependancy. The library can also be used to just create a multipart MIME message body. It also comes with a command line application for sending mail (with optional attachments).
Inbucket is an email testing service. It accepts messages for any email address and makes them available to view via a Web interface. It allows Web developers, software engineers, and system administrators to quickly see the emailed output of their applications. No per-account setup is required. Mailboxes are created on the fly as mail is received for them, and no password is required to browse the content of the mailboxes.