Make sure your email has a valid email address in the "From email" line.
If that doesn't fix the problem, ask your engineering team to white list Marketo's email IPs. See this help article for a full list of the IPs https://community.marketo.com/MarketoArticle?id=kA050000000KypECAS.
Whitelisting isn't a good idea if you want to have an idea of how your Marketo emails fare in the outside world. You might get them through to your team's test addresses that way, but that says nothing about your leads' mailservers.
The answer is for the IT team to determine what anti-spam or other check on their mailserver is preventing the mail from being accepted.
If you simply bypass the check, that ignores the fact that any other mailserver that performs the same check will not receive the mail.
Transmission problems due to anti-spam checks fall into three broad categories:
Well-known checks such as SpamAssassin rules, DNSBL lookups, etc. that use scoring that is within industry standards.
Outright misconfiguration, such as checking a blacklist that no longer exists or mishandling the return value from a check (scoring positive when it should be negative).
Non-standard, very strict checks that are done because of specific internal needs. In such cases it is made clear to everyone involved that their mailserver is not representative of the wider internet (in which case it cannot be used for testing anything except message layout).
Only in the case of  does whitelisting make sense, or else you're just covering up a problem that should be properly investigated. If I ever found myself forced to whitelist emails from Marketo I would stop using Marketo (luckily that has never happened!).
is there a quota on sending test emails to a specific user? I send test emails to user A - none are received and not in junk mail; however, I send that same test email to user B (I even tried sending to both at the same time), only user B receieves the email