Spam detection is not an exact science, and is done on the receiving end: no provider would ever be able to guarantee any email will not be detected as spam in all cases.

However there are many steps one can take to reduce chances of this happening.

On Edgefolio's side, we have taken as many steps as we can for email campaigns to have the best scores possible: the sending domain is properly registered and validated, our sending tools are the best in class in email marketing industry (using the Mailchimp backend), and the email template for the FundPortal campaigns are cleanly formatted and free of scripts that could affect spam scoring. Our email sending reputation is listed as "Excellent" with 97% deliverability (the other 3% attributed to bounced emails due to wrong recipient address).

In addition, the FundPortal campaign tool offers the options to set a nice Sender Name, a sane reply-to address, and more importantly to personalise the message to your recipient, using tags such as {{ first_name }}, {{ last_name }}, etc. 

There are many things that go into spam detection, and we try to take all the steps we can to improve the scoring. The content of the email message has a big impact on the score: avoid using generic greetings for example, such as "Dear Sir, ", and try to be personal instead.

Here is an article that lists the most important points to improve your campaigns in terms of spam detection: https://webengage.com/blog/how-to-avoid-spam-filters-when-sending-emails/
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That being said, if you know of particular examples of recipients who have not received an email, invite them to classify your email as "not spam" to improve your scorings in the long run.