Create a new account

Open iPhone Settings application and choose Mail, Contacts, Calendar:

Then select Add Account...:

DavMail is not an Exchange ActiveSync server, press Other:

Choose Add Mail Account:

Enter your name, email address and password, then press Next:

Select IMAP account type:

In Incoming Mail Server section, enter your DavMail server hostname, append ':' and port if DavMail IMAP port is not 143:

In Outgoing Mail Server section, enter your DavMail server hostname, do not append port, this is not supported by current iOS version, then press Next:

Wait until your iPhone has finished verifying all possible port/protocol combination:

If you get the Cannot Connect Using SSL message, just select Yes, you will just need to adjust account settings later.

Save the account:

Confirm:

Back to account settings page, still need to fix SMTP port if DavMail is not listening on default port 25, open account settings:

Open Account Info:

Open SMTP page:

Choose primary server:

Adjust SMTP port:

Back to Account Info, open Advanced settings:

Back to Account Info, open Advanced settings:

Enable SSL on IMAP port:

Mail setup is complete, proceed to iPhone Carddav setup