Each Mail-in-a-Box provides webmail and an IMAP/SMTP server for use with mobile devices and desktop mail software. It also includes contacts and calendar synchronization. The box also includes automatic DNS configuration, spam filtering, greylisting, backups to Amazon S3, static website hosting, and free TLS (SSL) certificates from Let’s Encrypt. Your box can host mail for multiple users and multiple domain names.

It implements modern mail protocols (SPF, DKIM, and DMARC) and the latest security best practices, including opportunistic TLS, strong ciphers, and HSTS. When enabled, DNSSEC (with DANE TLSA) provides a higher level of protection against active attacks. Exchange ActiveSync is also available as a beta feature.