| Price from | Free | — |
| Free plan | Yes | — |
| Free trial | — | — |
| Open source | — | — |
| Web | Yes | — |
| macOS | Yes | Yes |
| Linux | Yes | Yes |
| API | Yes | — |
| Self-hosted | Yes | Yes |
| Plans published | 1 | 0 |
| Spec score · Mail Server Software | 8.3 (#4) | 7.2 (#30) |
| Deployment | Citadel can run in Docker, through a Linux build script, from source, or via a hosting provider. | Postfix is built from source and runs on UNIX-like systems; operating-system and appliance vendors also distribute ready-to-run versions. |
| Purpose | Citadel is an email, collaboration, groupware, and content-management system. | Postfix aims to be fast, easy to administer, and secure. |
| Support | Support is provided through an active user and developer community, an online knowledge base, a support forum, and a mailing list. | The postfix-users mailing list is for questions, problem reports, and feature requests; non-member postings are silently discarded. |