Can't send email from android phone

[#1]

I have been happily using K9mail on my android phone forsome months now but just recently it has stopped sending emails, they languish in my outbox, never get into my sent folder and I get error messages saying they have not been sent. The incoming and outgoing server settings are identical to those in Mozilla Thunderbird on my laptop which is working fine. My association with Plusnet goes way back (1998 would you believe) and I am on the old free-online server.

As far as I know there have not been any upgrades to k9Mail, but then perhaps I would not be aware even if there had.

Any ideas anyone - please?

[#2]

@Notverytechie 

I use k9mail on my pixel-7, these are my settings

Incoming - imap.free-online.net port 993 encryption TLS/SSL
Outgoing - relay.free-online.net port 587 encryption STARTTLS

HTH

[#3]

On the phone, is the SMTP server configured to require authentication?

Is it using port 587?

Is the phone connected over the same WiFi as the laptop or is it connected over mobile data?

[#4]

Hello Townman and Dan the van, thank you for your quick responses.

SMTP srever authentication is set to normal password, and my username and password are correct

The phone is using the same wifi as the laptop, (I have not tried it on mobile data, our signal here is very poor so we make most calls over wifi)

Port number is 25 (I am on a Pop3 connection, not Imap)

As I say, it has been working fine and the laptop still works with the same settings.

What is involved with changing from Pop3 to Imap. Would I lose any emails?

[#5]

@Notverytechie 

These are the correct settings for pop3 (Encryption is recommended)

Incoming - mail.free-online.net port 995 encryption SSL/TLS

or

Incoming - mail.free-online.net port 110 for NO encryption

EDIT: POP3 is for receiving emails not sending

To add try using the relay settings I previously posted