Outgoing mail stopped working from Andriod phone

[#1]

Hi I'm using the standard Android email client on an HTC 620 which has been working fine for months. Just replied to 2 emails and they have failed to send due to "incorrect account settings". Checking the outbound settings I'm using replay.plus.net on port 25 which has been working fine until about15:30 when this issue has started. Anyone else experiencing this or have any suggestions?

[#2]

Is the outgoing server really replay.plus.net? Or is that a typo and it is relay.plus.net (which is correct). Could you check if the email app has updated with SSL/TLS being turned on? It needs to be off.

[#3]

yes that's a typo. It started working again about 2 hours later with no intervention. It was quite difficult to get it to authenticate when the phone was set up and suddenly started working by magic even though nothing was changed so it looks like the smtp setup is a bit flakey - never had any problems with other ISPs.

[#4]

Was the connection over WiFi or over 3/4G - or indeed some inferior level of mobile data service?  For example I frequently encounter issues with 'data' services where there is no 3G signal.
There are various issues with mobile networks.  In some locations (cells) sending email (to any ISP) does not seem to work at all.  I suspect that they are blocking SMTP ports.  I have noticed that in some locations emails will not send, but move a couple of miles away and they will send without difficulty.
Note for off-isp-network SMTP connectivity, you should be using port 587 rather than port 25.  I take it that you have configured the SMTP service to use authentication?