Like other good email services, Microsoft spends a lot of time on stopping spam.  But unlike other companies (like Cobourg Internet) they do NOT rely on third party companies to identify spammers.  They identify large numbers of emails arriving from a single source and call that spam - without looking at the actual content.  It may not be spam but they say it is just to be sure.  Often, that means they identify servers as sending spam when that is not the case.  Once a server is identified by them, all spam from that server is blocked that is addressed to Microsoft accounts like Hotmail, Live, Sympatico, Bell, Outlook, etc.  It only needs one user to be sending large quantities of email for the ban to be applied to all customers using the same server.

The short term solution is for me to ask Microsoft to lift the ban but that can take up to 48 hours although usually it's more like 12.  Once I hear of it happening, I apply straight away.  This has now happened twice.

The long term solution is for customers to NOT use their account for mass mailings - more than 50-100 at a time - and no more than perhaps 50 to Microsoft accounts.  Instead use Mail Chimp or a similar service.  Sign up for a Mail Chimp account (it's free), ask me to help if you want.  I have four Mail Chimp accounts - one for myself and three for clients.  A secondary advantage is that a Mail Chimp account complies with Anti-Spam laws which require opting in and an unsubscribe feature.

Note that this problem does not affect incoming email or email to other accounts. 

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