Nowadays mobile internet has become a common virtue. With a mobile device you can connect to the internet through other networks than your ISP at home, whether it is through Wifi hotspots, GPRS, UMTS, Wimax, or whatever other connections. Browsing the internet while connected to a strange network may not be too difficult, but it may well be a problem while sending and receiving your e-mail. Problems may be caused by the security measures taken by your own ISP and/or the host ISP you're using on the road. Especially the security settings of the latter may even vary as you connect to the internet using various different ways (different Wifi hotspots for instance).
This page tries to emphasize the potential problems you might encounter when you want to send and receive your e-mail on the road. It also contains some hopefully useful tips. I'll treat sending and receiving separately because both can pose different problems.
I strongly advise you to check your settings on some strange networks nearby in order to avoid disappointments when you really need your mail when you're far away. After all, trouble shooting is not easy when you're under pressure and far away from any help.
If, despite of your careful preparations, you find yourself in a situation where it is not possible to send or receiver your e-mail using the e-mail client on your mobile device you can always fall back on web-mail.
Most ISPs offer you a way to read/write your mails through a web interface.
This might not be the most convenient way, but can save you in case of an emergency.
Therefore be sure you have you're e-mail user name and password at hand when you're on the move.
Usually it is not a problem to receive your e-mail while you're connected through a strange network. Most ISPs allow you to receive your mail, even when you're not connected to their own network. However some exceptions exist, especially with the few remaining free ISPs. They usually do not charge any subscription fees, they earn their money through the telephone connection charges instead. Therefore it shouldn't be a surprise that they do not allow you all the normal benefits when you're not logged in on their network. In that case you will only be able to read your mail through a web interface.
Since you're connected to the internet over an untrusted network while you're on the move it may be a good idea to use encryption (POPS protocol) if your mail ISP provides it.
Most modern e-mail clients have an option to use secure mail reception somewhere hidden in the account settings.
It's not that your mail necessarily contains so much confidential information. It's more to protect your mail password from falling into the wrong hands.
Be careful when you're abroad and connect to the internet using your cell phone.
Unfortunately roaming fees are still extremely high.
It is not uncommon for 1 Mega bytes of data to cost €15 or more.
Therefore limit the maximum accepted message size to a few kilo bytes to avoid unpleasant surprises in case someone sends you a complete movie. Most e-mail clients have such an option. Usually you can also choose to download the mail headers only. After that you can select the mails you want to download completely.
Also do not receive your mail unattended while roaming using a cell phone network. You'll never know how much data you'll receive when you're not watching.
Usually you want your mail to remain on the mail server, just in case you need to archive some of them once you're home again.
Most e-mail clients have such an option.
Some will delete the mail from the server if you delete the mail locally.
Others will delete the mail from the server if you empty the deleted items folder locally.
An other way to allow you to read your mails on multiple machines is to use the IMAP protocol instead of the POP protocol. However not many ISPs offer that protocol to end users. If you want to use IMAP be sure to use it on all your machines. Otherwise a machine which still uses POP may empty your entire mailbox inadvertently.
Receiving e-mail was quite easy.
Sending e-mail over a different network than your own will prove a bit more tricky.
The reason is security and the attempts to reduce spam.
Obviously spammers try to remain anonymous, that's why they love to use other networks to send their junk.
When the internet was still young all users were trustworthy people. Outgoing mail servers were open to anyone who wanted to send a mail, just like with a normal mail box in the street. You didn't even have to authenticate yourself. Later this proved to be a bit naive when spammers started abusing those mail servers to send spam in all directions.
Unfortunately the original SMTP protocol, which is used to send mail, did not have any means to authenticate the user. Therefore some cunning plans were devised to make the SMTP protocol more secure.
Probably the simplest solution was to prevent relay services.
If you're connected to the internet through your own ISP you can send mail wherever you want, without authenticating yourself.
After all your ISP knows who you are.
But if you want to use the SMTP server of your ISP while you're connected to the internet through a different ISP you are only allowed to send mails to your own ISP's domain.
For instance if your ISP is called example.org, then you can send mail to email@example.com. However you can't send mail to firstname.lastname@example.org, because that is a destination in another domain. This technique reduced some spam, however with the rise of unprotected WLANs spammers could still deliver their evil goods quite easily.
Usually the return address set in your mail program should be a known mail address to your IPS's SMTP server.
Another technique is called POP before SMTP.
The principal is simple:
The user downloads his mail first, using the POP protocol.
To do that the user has to authenticate himself.
This sends a signal to the SMTP server to trust this computer/user combination for let's say the next 15 minutes or so.
Be aware that POP before SMTP is being depreciated. More and more ISPs will stop using this method. This should not be a problem with most modern e-mail clients. However you may start experiencing problems in particular with older PDA models which do not comply with modern SMTP authentication protocols.
In 1999 specialists have amended the SMTP protocol which now does allow direct user authentication.
See RFC-2554 for technical details if you like.
This renders the previous measures obsolete, which is why POP before SMTP is now being depreciated.
Some ISPs even offer you the opportunity to use encryption, together with SMTP authentication, to make the protocol even more secure. This way your e-mail password can not be stolen by spammers while you're logged in through an untrusted network.
The above topics should explain why you always have to use STMP authentication if you want to be able to send mail through a strange network. This is so important to set it right that it is well worth testing the settings on a strange network nearby before you leave. Simply login to a strange network, a public hotspot, someone else's Fon hotspot, an open Wifi network, or some cell phone connection and send a mail to a different ISP than your own. Then check if the mail really arrived. If it didn't you will probably get an error back from the server telling you that the message could not be sent, for whatever reason.
Recently I discovered that my cell phone provider blocked port 25 entirely. This means that you can not send mail to any SMTP server, except to the telco's own SMTP server. I can use the telco's SMTP server, but that would not work if I'm connected over Wifi. This would require me to change the SMTP server every time I change connection type. Needless to say that this is quite a nuisance. Fortunately there was quite an easy way around this, for me, by using an encrypted connection to my ISP's SMTP server. Encrypted connections use port 465 instead of the blocked port 25. But if your ISP doesn't support an encrypted SMTP server you're out of luck, then you'll have to use the telco's SMTP server and switch to another one if you're connected over Wifi.