Iphone email unable to send out

Hi KIEK ENG LI,

Welcome to the Apple Support Communities!

I know that it can be frustrating when an application as useful as Mail is not sending as your would expect from your account. In this situation, I would recommend working through the troubleshooting steps outlined in the attached article.

Get help with Mail on iPhone, iPad, and iPod touch - Apple Support

"Relaying denied" or "Email address rejected by the server" when you try to send email

This error indicates that either an email address is incorrect or your settings aren't correct for your current connection. Make sure the email address is correct for messages in the Outbox or try a different port:

If you're on a Wi-Fi network connected to the same network as your email domain, such as your Cable or DSL provider, try port 25:

1. Tap Settings > Mail, Contacts, Calendars.
2. Tap your email account, then tap Account.
3. Scroll down and tap Outgoing Mail Server.
4. Tap Primary Server, then tap Server Port.
5. Delete the current port and enter 25.
6. Tap Done.

When you connect to a cellular data or a different Wi-Fi network, you need to use an alternate port and authentication, if your email provider supports it. The most common alternate ports are 465 and 587. Check with your email provider for specific settings.

If you still can't send email, you can set up an alternate SMTP server.

Cheers,

Joe

Just found what may be a solution, if you have your iphone/ipad connected to a wi fi network it wont relay when I turn off wi fi it works fine using my cell data

Even I have the same issue. Tried the steps given by joe_7399. It does not work. PLZ HELP!!!!!!!!!!!!!!!!!!!!!!!!!!

if the network wifi or cell one is connected to does not allow the port the mail provider use to send mail in this case often port 25 then it will not work