Email Server

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  https://cr.yp.to/qmail.html/

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  https://wiki.qpsmtpd.org/

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  https://www.dovecot.org/

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  https://www.clamav.net/

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  https://spamassassin.apache.org/

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  https://www.maxmind.com/

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  https://letsencrypt.org/

A private open source email server provides unlimited configuration, customisation, and users, with no additional cost per user and mailbox size up to the available storage.

• DKIM Signed Email
• DMARC Policy
• SPF Policy
• DNSBL Blocklists
• RHSBL Blocklists
• URIBL Blocklists
• Whitelist / Blacklist
• Greylisting
• Spam and Virus Filtering
• GeoIP Filtering
• Multi-Domain
• Server Sieve Email Filtering
• Blind Carbon Copy
• SSL Encrypted IMAP + SMTP + POP3
• TLS Transport to Remote SMTP Hosts
• SSL Webmail with DAV Integration of Calendars, Contacts, Tasks
• Open Source Letsencrypt SSL Domain Verification Certificates, or Commercial SSL Certificates.

Koozali SME Server is free and open source – there are no limitations and you can inspect, integrate, extend and modify however you want.