If you have access to a course or project site, you can send mail to its Email Archive. (Some sites, depending on how their owners have configured them, also accept mail from non-participants.) Site members may choose to read the mail in the site's Email Archive, or they may choose to have it forwarded to their own accounts.
To send an email message, you may use whatever email client
you wish. Simply address the email message to your site's address or
alias. You will find this address and/or alias stated in your site;
Email Archive and look under "Email sent to the
following addresses will be archived and sent to participants:". Use
one of these addresses in the "To:" field of your email message.