As suggested by Adam Miller in the comments, I'll add another solution.
The MailMessage(String from, String to) constructor accepts a comma separated list of addresses. So if you happen to have already a comma (',') separated list, the usage is as simple as:
MailMessage Msg = new MailMessage(fromMail, addresses);
In this particular case, we can replace the ';' for ',' and still make use of the constructor.
MailMessage Msg = new MailMessage(fromMail, addresses.replace(";", ","));
Whether you prefer this or the accepted answer it's up to you. Arguably the loop makes the intent clearer, but this is shorter and not obscure. But should you already have a comma separated list, I think this is the way to go.