Mail is preferred email client of many mac users. One of the issues of using Mac Mail is the setting of reply to address. Particularly for users who have multiple accounts from providers like gmail and wish that their reply emails should go to their company address. There is a solution for users who have one account and wish to set a permanent reply-to address to all their emails. This can be done using the following solution.

http://email.about.com/od/macosxmailtips/qt/etalwaysreplyto.htm

However, for majority of users it may not be the best solution. Also for users of iPad and iPhone, the above solution will not help.

 Here is an alternative solution for users of gmail.

Gmail allows you to send your email from your desired email address using gmail smtp server. To activate that  option users should to account of setting and add the address in "send mail from another address". For example you can add user@company.com as the address. Gmail need this to verified by either clicking the link sent to that email or by providing the security code. 

Also, in your Mac Mail account (or to that matter any email clients in iPad, iPhone etc) setting make sure that you are using this user@company.com as email address in preferences-account information settings.