Email to Hotmail or Gmail goes to Junk / Spam folder
Some possible reasons that cause this issue:
a) IP not set with proper SPF or PTR records.
b) IP is blacklisted and classified as spamming IP.
c) High volume of emails goes to Hotmail /Gmail server from IP or source that Hotmail/Gmail users classify as Junk or Spam mail.
If any of the IPs were earlier blacklisted, it may take some time (estimate about 3-7 days) for Gmail and Hotmail spam filtering system to establish that your email gets valid messages. At the same time, you may request your Gmail/Hotmail user (recipient) to mark your emails as Not Junk or Spam.
For more information, you can check the following links:
Hotmail: [ http://mail.live.com/mail/junkemail.aspx ] –> SmartScreen
Gmail: [ https://support.google.com/mail/answer/81126 ] –> “Delivery”
KB: [ http://gmailblog.blogspot.com/2012/03/learn-why-message-ended-up-in-your-spam.html ]
For Hotmail Users-
Emails will still land in Junk Folder during the IP mitigation period or after IP blacklisting issue: please note that the Hotmail IP mitigation period will be 2 days (48 hours).
During this period, emails may land in the junk folder of Hotmail customers. Moreover, we recommend Users to click on “Not Junk” option in the email folder listed above to avoid future messages from landing in junk folder and to speed up the mitigation process.
See screenshot below – “Not Junk” option: