Trouble sending e-mails using OUTLOOK for MAC ;MAC I-PAD or I-PHONE.

I have the 3 devises MAC; I-PAD and I-Phone. My normal e-mail account was working fine then suddenly it stopped SENDING mail (I can still receive).

I am using OUTLOOK for MAC as my mail account.

My regular laptop works perfectly with all the same settings-it is only my apple devises.

I have attempted the following:

• Reboot.
• Checked all settings and changed both the smtp and the outgoing port.
• Contacted the various service provider who have checked all of their settings and all is fine.

I get an error message saying OUTLOOK CAN NOT FIND THE SERVER or SERVER CONNECTION HAS FAILED, but sitting right next to me the laptop is sending/receiving as normal.

Any ideas??