Can't send email on iPhone - Help.....

[#1]

I had the same issue using an iPhone 5 on Vodafone, namely, an inability to send email over 3G (works fine over wifi). I spoke to a few others at work with iPhones on vodafone, and they can send email over 3G without issues - key difference is that none fo them have Plusnet accounts. After a lot of net trawling and playing around, I finally got it to work by going to the Outgoing Mail Server field in my iPhone and entering the following under Other SMTP Servers: 'mail.vodafone.net'
Leave the 'Primary Server' as 'relay.plus.net' as that will be used when you're on wifi.

[#2]

I'm on Vodafone and authenticated email sends fine for me using relay.plus.net

[#3]

I have had this issue intermittently for ages. Email works fine over wifi. Sometimes works fine over 3G then randomly stops sending mail ("the recipient [email address] was rejected by the server". Also get error when trying to delete an email ("cannot send to trash"). 
I'm using iPhone 4, on vodafone, and only happens with my plusnet email account. Googling suggests deleting then adding email account again which sometimes works, but I shouldn't have to do that every week. It's weird how it just randomly starts happening without changing any settings.
Can anyone please help?!

[#4]

What port have you specified for outbound mail? If you're using 25 then try 587 and see if you have any more success with that. Also, bear in mind that certain 3rd party hotspots may have restrictions in place that cause problems.

[#5]

Quote from: martini42

Does anyone know anybody who has been able to send email from an iPhone on Vodafone (or any other big mobile phone network) via plus.net account without using wireless setting? Is it even possible? The support set-up pages suggest it is a breeze, however after many hours of configuration, re-configuration, checking and re-checking all settings, trying different ports, etc, it cannot be made to work. Plus.net telephone support were very helpful and patiently stayed with me while everything was checked and double-checked, but reading between the lines, I don't think they know how to make it work, and I suspect have never known an example of it working. So, if you're on the move, 'use gmail'!

Quote from: duncs

I have had this issue intermittently for ages. Email works fine over wifi. Sometimes works fine over 3G then randomly stops sending mail ("the recipient [email address] was rejected by the server". Also get error when trying to delete an email ("cannot send to trash").  Can anyone please help?!

Quote from: Bob

What port have you specified for outbound mail? If you're using 25 then try 587 and see if you have any more success with that. Also, bear in mind that certain 3rd party hotspots may have restrictions in place that cause problems.

Hi everyone,
I was responsible for some of the detailed revision of the iPhone how to configure email guide (specifically use of 'additional' mailboxes).  I have some 7 PlusNet email boxes across two PN accounts configured on my iPhone 4S (also previously on a 3S) with Orange (EE).  Note also that we have two iPhones and two iPads (as well as 2 PCs) all accessing the same PN email boxes at home and on WiFi hot spots... and it all works seamlessly.
Each uses only the emailbox's credentials (account+mailbox^$) for SMTP connection / authentication on port 25 and largely speaking everything works OK everywhare - that is at home on PN WifFi, out and about over 3G (etc) and in WiFi hot spots.  I say 'largely' as from time to time (since the merger of Orange & T-Mobile into EE) in some geographies it does not work over 3G.  I have observed that on a train journey from the NW to London, that sending email worked and did not work and then worked again through the journey.  Also in some WiFi hot spots sending does not work.
I therefore conclude that some phone providers (at cell level) and some WiFi providers are blocking SMTP port connectivity (25 ?) and this is not a PN problem nor indeed the configuration of one's iPhone settings.  What is assurred is that if you have not specified authentication credentials on the SMTP server it will never work if not connected to the PN network.
Specifying one's own carrier's SMTP server to get around this is not a good fix.  One needs to question the provider of why a correctly configured PN SMPT does not work - ask "What ports are you blocking?".

@Bob - What is the difference between port 25 & 587 in terms of acceptable use?  I guess that if a network provider blocks 25 on security grounds, then are they just as likely to block 587 as well?  Whilst tidying up this post I've just had a niggle that there might be additional SMTP access considerations if one has a non-subscription PN account - can you comment please?
@Martin42 - Ask Vodaphone if they have any restrictions on YOUR phone service access to 'other' SMTP services.
@Duncs - Which phone provider are you with?  Orange / T-Mobile / EE by any chance?  You might be seeing my train journey experience.
Cheers,
Kevin
^$ This is essential to avoid the need to give all emailbox users the password for the PN account - advice on the forums and indeed from PN support that one has to use the main account details for the SMTP server are not correct

[#6]

Hi
Just to add to the above, I'm on the vodafone network and both port 25 and 587 work on wifi and the mobile network on my iphone without any problems.
Dave

[#7]

This is a bit technical but here goes…
The main difference between sending mail via port 25 and port 587 is that authentication is mandated (in the RFCs (standards)) for port 587 whereas it is optional for port 25. However unauthenticated sending is classed as 'open relay' and most receiving MTAs (mail transfer agents) are likely to refuse mail from such relays (for spam prevention).
I believe Plusnet treat use of port 25 and port 587 equally. If connected via a Plusnet connection authentication is provided by login. If connected via a third part network with both port 25 and 587 Plusnet require the user to set up authentication in their email client. (This facility is available only for users with an active subscription account.)
Hence whilst an internet service provider (particularly mobile ones) might choose to block access to third party SMTP relays on port 25 as a spam prevention aid the case for doing the same with port 587 is fragile (because the relay should be using authentication). On this basis I would expect most mobile providers to allow mail via port 587 through.