• Can’t send emails using the Three mobile network – blacklisted IP address

    A client of mine brought this problem to my attention.

    One day, he could send emails from his Three 3G iPad fine, the next day emails could not be sent and stayed in the Outbox. The client asked for advice and tests were performed that indicated the mailbox was working fine, even when his iPad was incapable of sending mail. The tests performed involved sending message from our web-based email client because the mail server cannot differentiate between emails sent over a mobile connection, or a land-line connection.

    We looked at the usual issues with this sort of problem, like ports and SSL settings, but the settings for the iPad and our webmail system were identical and, as far as I was aware, compatible with the mobile network that was being used. Confirmation was sought from our hosting supplier and they confirmed that everything was setup correctly. As a result, I referred the client to Three and Apple for further information as there were no further tests we could perform that would result in a failure to send emails.

    Three weren’t very helpful at all. They simply told the client that they don’t support customer’s email connections and that the fault would be with the mailbox provider; end-of. Apple, on the other hand, spent some time with the client getting him to connect his iPad to Google and stating that if emails could be sent to Google, that proved that it must be the mailbox provider that was at fault.

    This has been going on for some time. Before Christmas I spent over four hours of my own time on a Sunday afternoon trying to resolve the issue, try all combinations of mail server address (our hosting provider has a few mail server address aliases for the same outgoing mail server), outgoing ports and other settings. Finally, we got the thing running and the iPad seemed to work for a couple of weeks. Then, after the Christmas period, the problem resurfaced.

    All the time during these trials and tribulations, the iPad never failed to send emails when it was connected to a land-line based broadband connection, a fact that had me telling the client that this has to be related to the mobile broadband provider. Unfortunately it was two-to-one and two very large organisations were telling him it was my mail servers that were at fault. Well I’d listen to them if I were him too.

    At one point, both Three and Apple told my client that you could not have the incoming and outgoing mail servers using the same address (e.g. mail.yourdomain.co.uk). Our mail servers always have done since 2077 and our hosting provider has hundreds of thousands of mailboxes, probably millions, all using the same address for the address for the incoming and outgoing servers. This is the point when I realised that my client was being dealt with by people that didn’t actually know how mail servers worked.

    In the end I worked with an engineer at my hosting company for three hours a couple of days ago to try and resolve this issue, sending emails in real-time and having him track them through the system. I must admit, I was expecting the emails not to arrive at my client’s mail server for delivery to the intended recipient, but to my surprise the tracking indicated that the emails were hitting the mail server and then being rejected; the mail server was refusing to deliver the mail we were sending on that morning even though they had been delivered fine the day before.

    It turned out that our supplier’s mail servers check the IP address from which mail is sent and compares it to the IP address blacklist maintained by Spamhauss, a leading organisation (used by the FBI no less) that maintains a list of IP addresses that have been used to send spam and spread malicious software. If it detects mail being sent from a blacklisted IP address it rejects the email for fear that it might be spam, or a malicious software delivery. This is very commendable and helps to prevent clients’ mailboxes from being used for dirty, underhand and illegal activities. Oh that Google, et. al., were so diligent; my client could send emails via Google’s Gmail service when he couldn’t through his own mail server.

    The IP address being used during these tests was 92.40.249.29, as allocated by Three’s DHCP servers when the iPad was connected to their mobile network. is a blacklisted IP address. To test the theory, the iPad was put into Airplane mode, to disconnect it from the mobile network, left for five minutes and then reconnected to the network. The next two occasions when I connected to the Three mobile network using this method a blacklisted IP address was issued again each time and I could not send emails whilst these IP addresses were allocated to my iPad.

    Later in the day I moved location, from Southport to Ormskirk and obtained an IP address that wasn’t blacklisted. Normal operation was resumed and emails could be sent without being blocked by the mail server.

    This morning we have the IP address 92.40.248.158 and this is not black-listed. Emails are flowing freely. So the problem has been resolved, now I’ve just got to get Three to admit to the problem and resolve it. I have started with them, but they are not willing to admit, at the moment, that the problem is anything to do with them. Please follow my post, Is Three Mobile Broadband support any good?, to find out how I get on with Three.

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