How many domains can be hosted on Exchnage 2010 ?

There is no maxium limit,
    --> But more domain means, more load on RAM.
    --> More certificate cost, as even if you go for SAN certificate, you can t add more than   10  fields to SAN.
    --> You may do trick by configuration of IIS redirection for 'AutoDiscovery' to reduce certificate cost.
    --> Link for IIS redirection for 'AutoDiscovery'
http://www.msexchange.org/articles-tutorials/exchange-server-2010/mobility-client-access/using-autodiscover-large-numbers-accepted-domains-part1.html

Even the Exchange 2010 can accept many domains, it can not send emails out from the respective domains ? Please clarify this ?

I just need to know whether we can manage desperate domains in the same Active Directory/Exchange server ?  Granting individual OWA to to any domains respectively.

When you say domains i assume its SMTP domains and your speaking of email flow. So no additional certs .. email flow would be as usual and adding Domains doesnt mean email-flow would increase until more users are added.

Whats spoken above in regards to Cert is more of AD domain and not sure how RAM would be affected in case of increase of STMP or AD domain

- Rancy

Thanks for the comments, I have one domain already operational in this server say www.domain1.com and now I need to add second domain in to the same server www.domain2.com. Both domains should operates like two separate email services.

Is this possible ?
And can I provide all the features respectively for each domain such as OWA ?

Thanks totallytonto, this would be a interesting reply, I would test this soon.

Thank again !