Mail works on WLAN but not on 3G or Edge

Question

Hello,
I am having a interesting problem with my iphone. My emails will not send i get a "failed to connect to SMTP" server or similiar error message, however, when i walk into my house, my emails are sent over my wlan. I can receive emails and i know my account settings are ok otherwise it wouldn't work over the Wlan, just not over my 3G connection which is what I really need to work, when I am at home I can use my macbook pro to send emails!
Help....!!

Answer 1

Is this email account provided by your internet service provider at home?
Most internet service providers block the use of SMTP servers that are outside of the ISP's network or not provided by the ISP unless the SMTP server is authenticated. When connected to the internet via the carrier's cell phone network is no different in this regard. These restrictions are in place as part of an overall effort to prevent spam emanating from the ISP's domain.
Most ISPs do not provide an authenticated SMTP server for the email account they include with monthly internet access.
If this email account is provided by your internet service provider, this is why you are able to send messages when connected to your wireless network at home since you are connected to your internet service provider's network when doing so.
If you are in the U.S., Apple includes AT&T's SMTP server on the iPhone for sending email with an account that does not have an authenticated SMTP server when connected to the internet via AT&T's cellular network.
Go to Settings > Mail, Contacts, Calendars.
Select the account.
Under the Outgoing Mail Server section, select the SMTP server selected to be used with your account.
Below the Primary Server section, there is an Other SMTP Servers section. If you are in the U.S., AT&T's SMTP server is available and probably turned off. Select the server and turn it on.
Below the Other SMTP Servers section, the following is provided when an additional SMTP server available is turned on:
If mail is unsuccessful using the primary server, it will try the other SMTP servers in succession.
This will take longer than usual since the primary SMTP server won't work when connected to the internet via AT&T's network. After sending is unsuccessful using the primary SMTP server, the 2nd SMTP server turned on will be used.
If this works, you can try using AT&T's SMTP server to send messages when connected to the internet via your ISP at home, but the same will likely apply in reverse. AT&T's SMTP server is not authenticated so your ISP at home will likely prevent you from being able to use this SMTP server when connected to the internet via their network.
I access two email accounts with my iPhone, and both have an authenticated SMTP server. I never have problems sending with either account regardless the ISP being used for my internet connection - via my wireless network at home, various wi-fi networks I have access to and frequent on occasion with different internet service providers, or when connected via AT&T's cellular network.