Safe sender periodically reverts to being flagged as spam in OUtlook 2010

Our phone system takes voicemail and sends it as an email to users with a WAV file attached. The email always comes from the same address ( Occasionally it will be flagged as Junk by Outlook. I have ensured that the email address in question is in the Safer Senders list which has fixed the issue in the past. However, after about 2 months, it begins going to Junk again, even though that address is still in the safe Senders (and safe recipients) list in Outlook. Has anyone else seen this before? If so, what fixed it?
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Amit KumarCommented:
Which version of Outlook you are using?
Install all required updates of Outlook.
You can deploy safesender list by group policy as well if it has to be applied globally.
ethbri4978Author Commented:
As stated in the title, 2010.

As stated in the description, the sender is already in the safe senders list.

And thanks for telling me to install updates, that's really (not) helpful.
Amit KumarCommented:
Go through with this article may help you. It can be issue when mail is coming to your domain and your anti spamming solution is marking mail with high SCL due to attachment. Allow respective attachment extension in content or attachment filter.

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Murali ReddyExchange ExpertCommented:
If you have a hygiene solution scanning your emails, mark it as a safe sender there. Generally the headers are updated with the spam scores based on the type/content and frequency of email being sent.

There is possibility that the email be categorized as bulk email or if the email contains links, non-office attachments like media files and foreign characters, there is a high possibility that your hygiene mechanism updates the spam score with a non-zero value.  This is done before the email reaching your outlook where is defined as safe sender.

This header info is read and categorizes the email to go to junk items folder.

You may try whitelisting the address on your hygiene solution
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