RainLoop is a webmail client that connects users to mail servers and provides an administrative panel for domains and configuration. A count-only ZoomEye query found 13,238 application matches and 81 title matches on 2026-11-04. The gap shows why one field cannot describe an internet-facing product population.
Measurement scope
The probes were app="RainLoop" and title="RainLoop" with sub_type=all, page 1, and pagesize 1 at 07:49 Asia/Shanghai. The application query returned 13,238. The title query returned 81. These are match counts in ZoomEye's selected global scope. They do not establish that every application match is an active webmail service or that every title match is a complete deployment.
RainLoop's configuration documentation describes an administrative panel at the ?admin route and domain configuration for the mail backend. It also documents a default administrator login in the product documentation. A default value is a deployment warning, not proof that any observed host still uses it.
The mail client is not the mail server
RainLoop presents a browser interface, while the IMAP and SMTP servers hold the mailbox and sending authority. A compromise of the webmail front end can capture credentials, read cached messages, or alter the mail configuration. The underlying mail server can also be exposed through a different hostname that the application count does not describe.
Review the admin route first. It should require a unique password, access from a management network, and a change from any documented default. Confirm that the admin panel is not reachable from the public internet unless there is a documented operational need. If the webmail client is public, enforce TLS and protect session cookies with appropriate flags.
Inventory domains and identity flows
The admin panel can add or configure domains. Each domain entry can contain an IMAP host, SMTP host, encryption setting, and credential policy. Review those records as configuration evidence. Remove stale domains and test that a disabled domain cannot still authenticate a user. Keep administrative changes in a log that records the operator and timestamp.
If the deployment uses a single sign-on or external identity provider, test both successful and disabled accounts. Check that a direct login route cannot bypass the intended policy. Review attachment limits, upload storage, and antivirus handling. A webmail client processes untrusted HTML and attachments, so browser security headers and content isolation matter.
Turn the count gap into a plan
The application field sees a large population that the page title does not. A title-only report would badly undercount the product. The application result is stronger for inventory, but it still needs ownership and version confirmation. Prioritize hosts with a certificate that matches the organization, a reachable login page, or an administrative route.
For each owned host, check the admin password, domain list, TLS configuration, and session policy. Then compare the finding with the mail server's own exposure. RainLoop is a useful example of a front end whose security depends on a backend that may sit on another hostname. ZoomEye identifies the web surface; the mail administrator has to verify the whole chain.
References
[1] RainLoop configuration documentation