When you send emails, there is a slight chance that it may end up in your recipient’s spam or junk folder rather than his/her inbox folder. It can be annoying as the intended recipients may miss out your important emails.

This can be due to the junk filtering rules configured by the recipient’s email service.

We could not change or control the rules set by the other email services. However, there are a few ways that we can do to avoid our mails from going into our recipient’s spam mailbox:

• Be registered in the contact list of your recipients.
• Avoid sending an email to a very long list of recipients in phased batches.
• Do not miss out the email's subject.
• Avoid using all CAPITALS, italics and colored font on email subject.
• Avoid using email subject with more than one exclamation point.
• Avoid using email subject or body that contains trigger words or phrases such as “free”, “you”, “yours”, “click”, “Viagra”, “porn”, “drugs”, “guaranteed win”, “urgent matter”, “limited-time offer”.
• Avoid using very large and colored fonts on the email body.
• Avoid attachments.

Reference: Chatterboxer’s Blog

If your emails are still being routed to your recipient's Junk folder, this is maybe because your email address could have been blacklisted(labelled as spam email) by the recipient. You may request them to whitelist your email address on their email system.