At Singapore Data Hub, we are very serious about email delivery and we are working our best to keep our customer email clean from being marked as spam or blacklisted.
Some customer ask, "Why do my email marked as spam while im not doing any email blasting, and im sending to recipient that actually having my email contact?"
Well, if you think that your email subject and content is clean, and your email is still marked as spam, we would suggest you to try checking on the IP address you are sending the email. If you are not logging into your email via webmail, you can find your ip address by going to google search, type "public ip". Google search will return you your IP address. Using the IP address, check from MXToolbox if the IP is blacklisted. If the IP is blacklisted, it might be the reason why your email is marked as spam.
To avoid this problem, you can submit your request to any spam server that blacklist the ip to remove the IP from blacklist, or you may use your webmail to send email instead of using email client like Outlook, Apple Mail. Of course, the best solution is to make sure your IP is not blacklisted. If the IP address is your office static IP address, you might want to submit blacklist removal request to spam servers to remove your IP from blacklisted.