Every cPanel email user reaches webmail through the server's cPanel service on port 2096 (or webmail.domain). As server administrator you decide which webmail apps are offered, how large attachments can be and how the IMAP server behaves. These settings are spread across a few WHM pages; this guide collects them.
Before you start
- Root access to WHM.
- Know what your users need: most only need Roundcube. Users learn it in how to use Roundcube.
Enable Roundcube and choose the default
- Open WHM → Server Configuration → Tweak Settings and filter for
webmail/roundcube. - Make sure Enable Roundcube webmail is On.
- Use WHM → Packages → Feature Manager to include Webmail and Roundcube in your feature lists. See Feature Manager.
- Save. Users can then set Roundcube as their default app on the webmail home screen.
Webmail proxy subdomains
On firewalled networks users often cannot reach port 2096. In Tweak Settings → Domains, keep Proxy subdomains and Proxy subdomain creation On so webmail.example.com works over port 443, and run Proxy subdomain override as recommended. Make sure AutoSSL covers the webmail subdomains; see AutoSSL in WHM.
Attachment and upload size
- The maximum message size accepted by Exim is set in WHM → Service Configuration → Exim Configuration Manager → Basic Editor → Mail → Maximum message size (around 50 MB is common). See Exim basics.
- Roundcube's upload limit follows the PHP settings of cPanel's internal PHP. In Tweak Settings → PHP, adjust cPanel PHP max POST size and cPanel PHP max upload size to match the message size.
Tip: Remember that encoding makes attachments about 33% larger. A 50 MB message size allows roughly 35 MB of attachments.
Dovecot (IMAP/POP3) settings
Open WHM → Service Configuration → Mailserver Configuration:
| Setting | Why change it |
|---|---|
| Maximum IMAP connections per IP address | Raise (e.g. 20–30) for offices where many users share one IP |
| Auth processes / login process limits | Increase on busy servers with many mailboxes |
| Allow plaintext authentication from remote clients | Keep Off; require SSL/TLS |
| Mailbox auto-expunge (Trash, Spam) | Set days to delete old Trash/Junk automatically and save disk space |
| Compress messages | On, to reduce disk usage on large mail servers |
Calendars and contacts
cPanel's calendar and contacts server (CalDAV/CardDAV on port 2080) is controlled in WHM → Service Configuration → Calendar and Contacts Configuration and the related feature in Feature Manager. Users connect as in CalDAV and CardDAV.
Troubleshooting
- Roundcube shows a database error: run
/usr/local/cpanel/bin/update-roundcube --force(on supported versions) or/scripts/upcp --forceto repair the installation. - Users locked out from an office: raise the per-IP IMAP limit and check cPHulk/firewall blocks; see cPHulk.
- Large attachments fail: align Exim message size and cPanel PHP upload limits.