| Price from | Free | Free |
| Free plan | Yes | Yes |
| Free trial | — | — |
| Open source | — | — |
| Web | Yes | Yes |
| macOS | Yes | — |
| Linux | Yes | Yes |
| API | Yes | Yes |
| Self-hosted | Yes | Yes |
| Plans published | 1 | 1 |
| Spec score · Mail Server Software | 8.3 (#4) | 7.9 (#18) |
| Deployment | Citadel can run in Docker, through a Linux build script, from source, or via a hosting provider. | Mailu runs as Docker containers and documents Docker Compose and Kubernetes deployment options. |
| Purpose | Citadel is an email, collaboration, groupware, and content-management system. | The project aims to provide an easily set up and maintained full-featured mail server without proprietary software or unrelated groupware features. |
| Support | Support is provided through an active user and developer community, an online knowledge base, a support forum, and a mailing list. | The project directs simple questions to its Matrix room, complex questions to GitHub discussions, and bug reports to GitHub issues; it describes itself as mostly developed in contributors' free time. |