Cannot send Photos using Yahoo email (smtp error)

With 2 seperate iPhones and 2 different yahoo addresses I have the same problem.

When trying to send photos, the message sits in the outbox for ages (a couple of minutes) and then gets an excalmation mark icon showing a failure to send - I also get an error message pop up that apple.smtp.mail.yahoo.com is not available.

Sending plain text emails is fine.

Doesn't matter what size photo is sent (choose actual size ~2MB or small ~50KB get the same failure).

The yahoo accounts have been deleted and recreated using the built in yahoo mail settings. Still fails.

I have tried to create a new Yahoo account using the IMAP settings in yahoo help which uses a different outgoing mail setting (smtp.mail.yahoo.com) which after soem minutes for the account to sync and show folders and content in the mail app, does send the photos succesfully.

However, I couldn't set the "DRAFTS", "SENT" and "TRASH" folders in the settings page to be on the server (the settings page showed only "INBOX" on the server which was greyed out - it didn't pull back the IMAP folder list for me to choose the right places so these folders would be phone only for sent mail etc. which isn't workable).

I cannot chage the outgoing mail settings for the built in yahoo account settings as they are greyed out as uneditable.

It seems that the apple specific yahoo SMTP outgoing mail server is failing.

Anyone got any ideas? how can I get my yahoo accounts configured without using the built in settings?

(to save the suggestions of getting a proper email service, I use gmail myself but my wife prefers yahoo so changing to gmail or other isn't an option, unless it can be behind the scenes? can I use google smpt but save the sent items in yahoo folders? I guess not)

Anyone else having this? it's relitavly recent and is intermittent (repeated attempts can get the mail sent sometimes) but mostly it fails.

I have tried having the working smtp server settings as a fallback for the built in configured yahoo mail but it still fails so doesn't seem to use the fallback option.

Yahoo mail is set to PUSH.

Yahoo accounts are UK (.co.uk) and Germany (.de)

iPhones are fully up to date (but it was happening on one phone at iOS4.x too prior to being upgraded

thanks

Lee