Microsoft Exchange server is a mail server created by Microsoft. It's possible to host your website at DreamHost but still use Microsoft for email. This requires you to set up a few DNS records. This article explains what needs to be adjusted.
On January 19 2017, DreamHost updated the SSL certificates on all mail servers. Because the SSL certificate was updated, you will see a message next time you open your mail client. This message will ask you to accept the new certificate. This certificate is completely safe for you to accept. Once your mail client saves the new certificate, your email client will function normally again. View the following article for further details:
Finding your DNS settings
The following assumes your Nameservers are controlled at DreamHost.
When you create your Exchange account, you are given specific DNS records. These can be added in your DreamHost panel. The following link is a general overview of what records Microsoft may give you:
Once you have the list of DNS records from Microsoft, enter them into your DreamHost panel. The following article walks you through how to create different types of Custom DNS records.
View the following article for information on how to change your MX records:
Once you have added your custom DNS records, they must then update online. This can take several hours. View the DNS propagation article for details. You can also check online at a site such as this: