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Your recommendation --&gt; &nbsp;SMTP port – use port 26 (instead of the default 25) for outgoing mail ... was the answer. The client can now access his email. Thanks.
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Outlook email can only send to primary done emails: I.E. - &nbsp;myemail@myemail.com ... but no other &nbsp;. User gets the following error message ... &quot;503 valid RCPT command must precede the message&quot; ... when sending to other email addresses outside their primary domain email address. This happens on user's desktop machine.
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Outlook email can only send to primary done emails: I.E. -  myemail@myemail.com ... but no other  . User gets the following error message ... "503 valid RCPT command must precede the message" ... when sending to other email addresses outside their primary domain email address. This happens on user's desktop machine.

Outlook email can only send to primary done emails: I.E. -  myemail@myemail.com ... but no other

An email client, email reader or more formally mail user agent (MUA) is a computer program in the category of groupware environments used to access and manage a user's email. A web application that provides message management, composition, and reception functions may internally act as an email client; as a whole, it is commonly referred to as webmail. Likewise, email client may be referred to a piece of computer hardware or software whose primary or most visible role is to work as an email client. Email clients can also have other systems, like calendars, notes and contact managers.