Outgoing email not maintaining font selection

Question

When I send out email, my 'Mail' (4.4) program is substituting Times New Roman for Arial fonts in the message text. When I eliminate a 'signature', the font remains Arial. If I create the 'Signature' in Arial, both the 'Signature' font and message font revert to Times New Roman. I have selected Arial as the default font for the message text.
Is there a email editor default setting? by the way, the recipients are all using Outlook for Windows and they have checked their Word Email editor settings.
They have indicated that the style that shows up is 'Apple-Style-Span'

Answer 1

According to this posting https://discussions.apple.com/message/9518120#9518120 you are sending the mail as plain text, and it is the recipient's Outlook that chooses to display plain text in Times New Roman.
Just a note from those of us who are somewhat visually impaired:  when you send an email to someone who has vision problems, the ability of the recipient to READ your email is dependent upon allowing the recipient to SET the preferences on the recipient's email so that the recipient CAN read the email. 
If pkuser's company has a policy of forcing their employees to send email out in a format which is inaccessible to the disabled, perhaps they should revisit their policy.  At best it is obnoxious, and it is a poor business practice to force your employees to be obnoxious in the company's name to customers, colleagues, etc.  At worst it can get the company sued.