MailSystem 是一个 .NET 平台开源的邮件处理组件，支持 SMTP, POP3, IMAP4, NNTP, MIME, S/MIME, OpenPGP, DNS, vCard, vCalendar，反垃圾邮件，查询合并等功能。如果要在非 GPLv3 软件使用，必须获得商业许可。

Common features:

• Asynchronous operations
• Secure connections using SSL
• Mail signing & encryption/decryption using S/MIME & OpenPGP
• Separate object for the Message and the clients
• Fully Accessible Headers
• Mail encoding customization for globalization
• Determine if it is a mail server bounce + e-mail address parsing
• Send from / receive Message object to file and streams

SMTP - Simple Mail Transfer Protocol

• Direct sending of e-mail without an SMTP server
• MX server caching (increase by 6 the performance of direct send)
• Mail queueing systems support
• Multiple bodies (both HTML and Text)
• Embedded Objects such as Image, Sound and Video
• Redundant SMTP Server List (fail over)
• Secure Authentication

POP3 - Post Office Protocol 3

• View Mailbox Size and Message Count
• Download Full Message or Header Only
• Secure Authentication

IMAP4 - Internet Message Access Protocol 4

• Manage Mailboxes (list, create, rename, delete, move, empty, etc.)
• Manage Messages (retrieve, copy, delete, append, etc.)
• Download Full Message or Header Only
• Manage flags
• Extended search features
• Secure Authentication
• New message arrival notification support (IDLE command)

NNTP - Network News Transfer Protocol

• List News groups and Articles Easily
• Download Full Articles or only Headers
• Secure Authentication
• Mail merging and template
• Load Configuration from XML or Text File
• Field formatting
• Bind Bodies with Data Sources (DataTable, ArrayList, Custom collections, ...)
• Bulk Mailing from a Data Source (in addition to the multiple data bound bodies)

vCard & vCalendar

• Contact file reading and writing
• Calendar event reading and writing
• Sending and receiving a meeting request

Anti-Spam

• Block list servers support (RBL)
• Full DomainKeys implementation
• Learning Bayesian filter
• Email Addresses Validation Using MX Record Caching
• Commtouch® anti-spam technology support

DNS

• Support for individual queries of all types
• Get mail exchange (MX) records of a DNS server
• Get all records from a DNS server

WhoIs

• WhoIs server querying
• Asynchronous mode
• Domain name availability check
• Custom WhoIs server list resource file support

项目主页：http://www.open-open.com/lib/view/home/1435844115591