Can send, but cannot reveive email

I have been hunting around the forums and although there are ample threads that relate to issues with email transport, I have been unable to find a solution. For me, I am able to send emails, but when trying to receive emails, the email doesn't appear to exist and there are no errors in the mail.err log or anywhere else that I can see.

This is a fresh install of virtualmin, installed using the install.sh file yesterday. I have tried installing it on two fresh debian 8 servers and in both cases the same issue happens. The steps I am taking:

• build a fresh server (my servers are hosted inside of vultr.com)
• install virtualmin
• set up a virtual site, for testing purposes I have only checked the "mail for domain enabled" feature. The only other thing I change from default is setting it to use the shared ipv6 address
• set up the email user. I leave everything as default, only setting the username and password
• from either roubdcube or the build-in usermin mail, I send an email to myself, it works no problem
• i try and reply to the email, or send an email directly to the email account set up in virtualmin and it fails

I don't see any errors in mail.err, I do however see this at the time of the email being sent, within mail.log:

Nov 1 14:11:43 dev dovecot: imap-login: Login: user=<info.jadoku.com>, method=PLAIN, rip=::1, lip=::1, mpid=2609, secured, session=<vRqIc+xczgAAAAAAAAAAAAAAAAAAAAAB> Nov 1 14:11:43 dev dovecot: imap(info.jadoku.com): Disconnected: Logged out in=50 out=469

So nothing particularly useful...

A couple of additional notes:

• when I look in the settings for a virtualmin > Edit Users > [select the above user] > Email Settings, it shows me that the inbox mail file exists in /home/jadoku.com/homes/info/Maildir. The "new mail received" time shows the creation time of the user, which I assume suggests that it's never registered an incoming mail?
• there was a thread that suggested disabling and enabling the dovecot socket, doing that doesn't seem to have done anythign
• config check is fine

Any suggestions on how I can sort this would be much appreciated.