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SPF set up OK? <br />
DKIM? <br />
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An SPF mismatch will certainly cause significant problems with email being blocked as spam. &nbsp;no SPF will have a smaller effect. Mismatched DKIM will also cause issues, but having no DKIM set up won't make much difference. <br />
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There are a number of services that can test emails for potential &quot;spaminess&quot;, it would be a good idea to send to one of these from within your app, and see what it reports back. <br />
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Go to <a href="https://www.mail-tester.com/" rel="ugc">https://www.mail-tester.com/</a>&nbsp;follow the simple instructions, and see what gets reported back.
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SPF set up OK?
DKIM?

An SPF mismatch will certainly cause significant problems with email being blocked as spam.  no SPF will have a smaller effect. Mismatched DKIM will also cause issues, but having no DKIM set up won't make much difference.

There are a number of services that can test emails for potential "spaminess", it would be a good idea to send to one of these from within your app, and see what it reports back.

Go to https://www.mail-tester.com/ [https://www.mail-tester.com/] follow the simple instructions, and see what gets reported back.

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Yes, gmail did respond with 220
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We are not able to send emails to gmail from an internal application server. &nbsp;Other external emails do accept the messages. &nbsp;Does anyone know what may stop this ? &nbsp;I have tested blacklisting and it doesnt show it is.
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We are not able to send emails to gmail from an internal application server.  Other external emails do accept the messages.  Does anyone know what may stop this ?  I have tested blacklisting and it doesnt show it is.

smtp question

Interactions between email servers and clients are governed by email protocols. The three most common email protocols are POP, IMAP and MAPI. Most email software operates under one of these (and many products support more than one).  The correct protocol must be selected, and correctly configured, if you want your email account to work.

Email Protocols

An email client, email reader or more formally mail user agent (MUA) is a computer program used to access and manage a user's email. A web application that provides message management, composition, and reception functions is sometimes also considered an email client, but more commonly referred to as webmail.