How to set up iPhone 5 iOS 6 email with IMAP over SSL on a custom port?

Question

Basically I have the same problem as this guy 5 years ago but the thread contained no useful answer. Maybe there are people out there who became smarter in the meantime? Please help me out how to get my iPhone read emails via IMAP over SSL on a custom port to the corporate server. The issue is that the iPhone only seems to work if you use the standard 993 port for IMAPS, not with a custom port as we have. I've installed the corporate root certificate in a profile, and it shows up as trusted and verified in the phone, so that should not be the issue. The mail app in the iPhone tries to connect, I can verify that from the server, but then does nothing, doesn't try to authenticate, doesn't log out, nothing is going on, and then drops the connection after 60 seconds. Repeats this every 5 minutes (as set to fetch e-mail every 5 minutes.)
Original thread 5 years ago: https://discussions.apple.com/message/8104869#8104869

Answer 1

Solved it by some (a lot) of fiddling.
Turns out it's not a bug in the iPhone, it's a feature.
Here's how to make it work.
DOVECOT
If the IMAPS port is anything other than 933 (the traditional IMAPS port) the iPhone's Mail App takes the "Use SSL" setting on the IMAP server as 'TLS', meaning it starts the communication in plain text and then issues (tries to issue) the STARTTLS command to switch the connection to encrypted. If, however, Dovecot is set up to start right away in encrypted mode, the two cannot talk to each other. For whatever reason neither the server nor the client realizes the connection is broken and only a timeout ends their misery.
More explanation about SSL/TLS in the Dovecot wiki: http://wiki2.dovecot.org/SSL
So to make this work, you have to set Dovecot the following way. (Fyi, I run Dovecot 2.0.19, versions 1.* have a somewhat different config parameters list.)
1. In the /etc/dovecot/conf.d/10-master.conf file make sure you specify the inet_listener imap and disable (set its port to 0) for imaps like this:
service imap-login {
  inet_listener imap {
    port = --your port # here--
  inet_listener imaps {
    port = 0
    ssl = yes
This of course enables unencrypted imap for all hackers of the universe so you quickly need to also do the things below.
2. In the /etc/dovecot/conf.d/10-ssl.conf file, make sure you set (uncomment) the following:
ssl = required
This sets Dovecot to only serve content to the client after a STARTTLS command was issued and the connection is already encrypted.
3. In /etc/dovecot/conf.d/10-auth.conf set
disable_plaintext_auth = yes
This prevents plain text password authentication before encryption (TLS) is turned on. If you have also set ssl=required as per step 2, that will prevent all other kinds of authentications too on an unencrypted connection.
When debugging this, please note that if you connect from localhost (the same machine the server runs on) disable_plaintext_auth=yes has no effect, as localhost is considered secure. You have to connect from a remote machine to make sure plain text authentication is disabled.
Don't forget service dovecot restart.
To test if your setup works as it's supposed to, issue the following (green) from a remote machine (not localhost) (I'm using Ubuntu, but telnet and openssl is available for almost all platforms) and make sure Dovecot responds with something like below (purple):
telnet your.host.name.here yourimapsportnumber
* OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE STARTTLS LOGINDISABLED] Dovecot ready.
Most importantly, make sure you see 'STARTTLS' and 'LOGINDISABLED'. Then issue STARTTLS and hopefully you see something like this:
a STARTTLS
a OK Begin TLS negotiation now.
(The 'a' in front of STARTTLS is not a typo, a prefix is required by the IMAP server in front of all commands.)
Close the telnet (with 'a logout' or Ctrl+C) and you can use openssl to further investigate as you would otherwise; at the end of a lot of output including the certificate chain you should see a line similar to the one below:
openssl s_client -starttls imap -connect your.domain.name.here:yourimapsportnumber
. OK Pre-login capabilities listed, post-login capabilities have more.
You can then use the capability command to look for what authentication methods are available, if you see AUTH=PLAIN, you can then issue a login command (it's already under an encrypted connection), and if it's successful ("a OK Logged in"), then most likely your iPhone will be able to connect to Dovecot as well.
a capability
* CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE AUTH=PLAIN
a login username password
* CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS MULTIAPPEND UNSELECT CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS
a OK Logged in
POSTFIX
Likewise, you have to set Postfix to wait for STARTTLS before encrypting the communication.
1. You have to delete the setting smtpd_tls_wrappermode=yes from /etc/postfix/master.cf and/or /etc/postfix/main.cf, if it was enabled. This will mean Outlook won't be able to connect any more because it requires a TSL connection without issuing STARTTLS as per Postfix documentation (haven't tested.) In my case we don't use Outlook so I didn't care. Outlook + iPhone + custom SMTPS port are simply not possible together at the same time as far as I understand. Pick one to sacrifice.
2. Require encrypted (TLS) mode for any data transfer in /etc/postfix/main.cf:
smtpd_tls_security_level = encrypt
3. Authentication should only happen while already in encrypted (TLS) mode, so set in /etc/postfix/main.cf:
smtpd_tls_auth_only = yes
Don't forget postfix reload.
To test if this works, issue the following telnet and wait for the server's greeting:
telnet your.host.name.here yoursmtpsportnumber
220 your.host.name ESMTP Postfix (Ubuntu)
Then type in the EHLO and make sure the list of options contains STARTTLS and does not include an AUTH line (that would mean unencrypted authentication is available):
ehlo your.host.name.here
250-STARTTLS
Then issue starttls and wait for the server's confirmation:
starttls
220 2.0.0 Ready to start TLS
Once again, it's time to use openssl for further testing, detailed info here http://qmail.jms1.net/test-auth.shtml
CERTIFICATES
You also need to be aware that iOS is somewhat particular when it comes to certificates. First of all, you have to make sure to set the following extensions on your root certificate (probably in the [ v3_ca ] section in your /etc/ssl/openssl.cnf, depending on your openssl setup), especially the 'critical' keyword:
basicConstraints = critical,CA:true
keyUsage = critical, cRLSign, keyCertSign
subjectKeyIdentifier=hash
authorityKeyIdentifier=keyid:always,issuer:always
And then on the certificate you sign for your mail server, set the following, probably in the [ usr_cert ] section of /etc/ssl/openssl.cnf:
basicConstraints=CA:FALSE
keyUsage = nonRepudiation, digitalSignature, keyEncipherment
subjectKeyIdentifier=hash
authorityKeyIdentifier=keyid,issuer
subjectAltName = DNS:your.domain.name.here
issuerAltName=issuer:copy
Please note, the above are results of extensive google-ing and trial and error, so maybe you can omit some of the stuff above and it still works. When it started working for me, I stopped experimenting because figuring this all out already took way too much time. The iPhone is horribly undocumented when it comes to details of its peculiar behaviors. If you experiment more and have more accurate information, please feel free to post here as a reply to this message.
You have to import your root certificate into your iPhone embedded in a profile via the iPhone Configuration Utility (free, but only available in Windows or a Mac; details here: http://nat.guyton.net/2012/01/20/adding-trusted-root-certificate-authorities-to- ios-ipad-iphone/ ), after having first added it to Windows' certificate store as a trusted root certificate. This way the Utility will sign your certificate for the phone and it becomes usable; if you just add it from the phone it will be there but won't be used. Using a profile has the added benefit of being able to configure mail settings in it too, and that saves a lot of time when you have to install, remove, reconfigure, install again, etc. a million times until it works.
Another undocumented constraint is that the key size is limited to a max of 4096. You can actually install a root certificate with a larger key, the iPhone Configuration Utility will do that for you without a word. The only suspicious thing is that on the confirmation screen shown on your iPhone when you install the profile you don't get the text "Root Certificate/ Installing the certificate will add it to the list of trusted certificates on your iPhone" in addition to your own custom prompt set up in the iPhone Configuration Utility. The missing additional text is your sign of trouble! - but how would know that before you saw it working once? In any case, if you force the big key certificate on the device, then when you open the Mail App, it opens up and then crashes immediately. Again, without a word. Supposedly Apple implemented this limit on the request of the US Government, read more here if you're interested: http://blogs.microsoft.co.il/blogs/kamtec1/archive/2012/10/13/limitation-of-appl e-devices-iphone-ipad-etc-on-rsa-key-size-bit.aspx .
IN CLOSING...
With all this, you can read and send email from your iPhone.
Don't forget to set all your other clients (Thunderbird, Claws, etc.) to also use STARTTLS instead of SSL, otherwise they won't be able to connect after the changes above.