Important on ZevsHost servers: outbound SMTP ports 25, 465 and 587 are closed by default on VDS — this keeps the network clear of spam. The direct delivery described below will not work on a fresh server, and neither will external relays over SMTP. We open the ports for established customers on request through support, case by case. If you need mail right away, send it through your provider’s HTTP API: it runs over 443 and is not affected. Shared hosting and dedicated servers have no such restriction.

ISPmanager 6 sets up the mail server (Exim + Dovecot) automatically. Creating a mailbox takes just a few seconds.

Creating a mailbox

Mail → Mailboxes → Create.

Field	Description
Name	The part before @ (info, admin, support)
Domain	Your domain
Password	Password for IMAP/SMTP connection
Quota	Mailbox size limit (MB)

Mail client settings

Protocol	Server	Port	SSL
IMAP	mail.example.com	993	SSL/TLS
POP3	mail.example.com	995	SSL/TLS
SMTP	mail.example.com	465	SSL/TLS
SMTP (STARTTLS)	mail.example.com	587	STARTTLS

Setting up DKIM

Mail → Domain settings → select the domain → DKIM → Enable. ISPmanager will generate a DKIM key and show the TXT record to add to your DNS.

✅ Without DKIM, emails from your server will land in spam for most recipients. Enable DKIM right after setting up mail.

Creating a forwarder

Mail → Forwarders → Create. Specify the source address and the destination address.

SpamAssassin (anti-spam)

Mail → Domain settings → select the domain → Anti-spam → Enable SpamAssassin. Configure the threshold (default 5) and the action (tag / delete).

Webmail (Roundcube)

ISPmanager includes Roundcube. Access it at: https://mail.example.com or via Panel → Mail → Webmail.

⚠️ For mail to work correctly, make sure your domain's DNS has MX records pointing to your server, and that a PTR record (reverse DNS) is configured through your hosting provider.

Common Mail Errors

Message	What it means
550 5.7.1 Relay access denied	The outbound mail port is closed by default on VDS (see the notice above), or the client didn't complete SMTP AUTH
Certificate name mismatch in the mail client	The connection targets mail.example.com, but the SSL certificate only covers example.com without a matching alias
DKIM: neutral or fail in message headers	The DKIM TXT record wasn't added to DNS, or it hasn't propagated yet
Too many connections during sync	Too many IMAP connections are open at once from different devices to one mailbox

IMAP vs POP3: Which to Choose

Criterion	IMAP	POP3
Sync across devices	Full — folders and read status are shared	None — each device downloads separately
Where mail is stored	On the server	Usually locally after downloading
Mailbox quota	Used continuously	Freed after downloading
Recommended port	993	995

When ISPmanager's Built-in Mail Isn't Enough

You need to send to thousands of addresses with open tracking — that calls for a dedicated email-sending service, not a hosting mailbox
You need high IP reputation for B2B campaigns — outbound mail from a shared hosting IP isn't suited for that
You need integration with corporate Exchange or Google Workspace
You need a years-long mail archive with full-text search across attachments

Verifying the Result

After setting up the mailbox, confirm the certificate and ports actually work:

# Check the certificate on the IMAP port
openssl s_client -connect mail.example.com:993 -quiet

# Check that SMTP responds and presents the right name
openssl s_client -connect mail.example.com:465 -quiet

If openssl s_client drops with a certificate error, go back to the DKIM section and confirm that mail.example.com is actually covered by the domain's SSL certificate. Related topics: configuring Postfix on a VDS and sending WordPress mail through SMTP.

Mailbox Quotas and Limits in Practice

A mailbox quota in ISPmanager is calculated from the actual size of stored messages on disk, attachments included, not the number of messages. Once the limit is hit, new incoming mail is normally rejected server-side with code 552 "Mailbox full" — the sender gets a bounce notice rather than a silent loss. It's worth explaining this to clients in advance: complaints of "mail isn't arriving" usually turn out to be a full mailbox, not a DNS or spam-filter problem.

Domain Mail Reputation: SPF and DMARC Alongside DKIM

DKIM only closes part of the deliverability problem. Stable domain reputation needs all three mechanisms together: an SPF record lists which servers are allowed to send mail on the domain's behalf, and DMARC tells the receiving server what to do when SPF or DKIM fails. ISPmanager 6 usually offers ready-made SPF and DMARC templates alongside DKIM on the same domain settings screen — don't skip those two fields and stop at DKIM alone.