My computer has just stopped sending hotmail messages via Thunderbird. I have been to the THUNDERBIRD help topics and all of the server settings are exactly as they should be. The error message is as follows:

Alert - an error occurred sending mail: SMTP server error. The server responded. 5.5.4 Invalid Address contact you mail administrator for assistance.  

Firstly I have no idea how to contact my e mail administrator and secondly I have no idea how to sort the problem. Any advice needs to be simply put. I am not smart technically speaking. I am working on a mac, not sure if that matters?

Thanks
Hi I'm Hernan, I'm mail administrator of ELSERVER.COM, we are having some issues with a reception of hotmail's accounts. Our clients sent us email from "@hotmail.com" account and they don't receive it, or, they receive very delayed, typically by about 12 hours.
We had verified our filters and restriction policies and didn't found any problem.
We check a mail's headers and we figured out that a delay was produced in your servers, if you need a headers i could provide these.

We keep in touch

Best Regards
Hi Hotmail Team!  I cannot foward emails that I received to other contacts.  They all came back with a messege from the Mail Administrator saying "mail system error-returned mail" What is going on?  Is this because I deleted over 12,000 messages that were cluttering my inbox last night and then had to delete them from my delete box today?  In between, I had Norton Easy Support help me with my computer because it went down last night and wouldn't start.  But that had nothing to do with any emails.
Hi, I've received the following message: 
Attention FINAL WARNING
 Error Code: 609 
E-mail Services Mail Administrator  

 Dear Customer,  This is an automatic message from our server as a final reminder; If you no longer wish to use your e-mail account, then you can safely ignore this email. If you do want to keep your account active, then simply update the error code below;   

Error 609   

We apologize for any inconvenience and appreciate your understanding.  
Regards Mail Administrator. 

When I click on ERROR 609 it takes me to Windows 8 and Windows Server 2012 cumulative update: November 2012 - an article. 

I can't understand what I need to do next. Please help! Thanks.

Maria.