Security Issues with Apple Mail and Safari on Yosemite 10.10.2

I have recently upgraded to Yosemite 10.10.2 and since then I have had difficulty with Gmail and IMAP accounts, and now web browsing with Safari.

Gmail:

I am constantly receiving email notifications from Gmail stating:
'We recently blocked a sign-in attempt to your Google Account, Date/Time/Location/...If it was you you can switch to an app made by Google such as Gmail to access your account...or change your settings so that your account is no longer protected by modern security standards'.

IMAP:

I have changed geographic locations since upgrading to Yosemite. Now that I am in a different country I cannot send emails via my IMAP accounts. I receive the following error message from Apple Mail when trying to send an outgoing message:

'Cannot send message using the server xxxxxxxxxx.xx. An SSL error has occurred and a secure connection to the server cannot be made'. Changing email accounts results in the same problem.

WEB BROWSING WITH SAFARI

Pages are very slow to load, usually one minute minimum before I see more than a white page. I also use Chrome, without an issue. Now I have moved countries I am getting security verification messages from Google when searching: 'Google has detected suspicious activity from your computer. Please enter the Captcha information to continue....'

I do regular security checks on my Macs, there are no known issues either of them.

Any help appreciated.