I work for a construction company with about 160 users. Most information is organized by project, but some employees still keep personal Outlook PST files—either because they may need the messages someday or because they do not want to clean up and file them properly.
Our backup footprint keeps growing. I trust air-gapped tape backups most, and we currently use LTO-7 cartridges with roughly 6 TB of usable capacity, but we are reaching the limit. We also maintain immutable backups in Wasabi, although I would prefer to keep tape as part of our recovery strategy.
How do other organizations handle personal PST files? Do you prohibit them, migrate them into Exchange Online Archive, or use a separate archiving product? If online archives are used, do you back them up as well? My preference would be to keep normal mailboxes around 100 GB, require valid project-related messages to be stored with the project data, and have users delete anything unnecessary.
5 Answers
Your 100 GB guideline is reasonable for ordinary mailboxes, but retention should be driven by business and legal requirements rather than an arbitrary size limit. Project correspondence that has lasting value belongs with the project records, while routine mail can follow normal retention rules. Also check whether your tape software can span a backup across multiple cartridges; reaching the capacity of one cartridge does not necessarily mean abandoning tape.
A third-party archive such as MailStore can work if you want a dedicated searchable archive that is then backed up normally. Some organizations leave only recent mail in Outlook while the archive holds older messages. It is still important to define retention and ownership rules, since an archive should not become an unlimited dumping ground.
The cleanest approach is to import existing PSTs into Exchange Online or the users' archive mailboxes, verify that the imports completed, and then block creation of new PSTs through policy. Users can still search old messages without keeping huge files on laptops, file shares, or synchronized cloud folders. Check your licensing before relying on auto-expanding archives, and make sure your backup product includes archive mailboxes and can restore them.
That is close to the direction I am considering. I mainly want to avoid moving the problem from PST growth to unprotected online archive growth.
Do not treat PSTs as an acceptable backup method. If users have valid historical mail, bring it back into the managed mail system or a controlled archive, back that archive up according to your retention obligations, and prevent PSTs from being synchronized through services such as OneDrive. That gives you centralized search, retention, auditing, and predictable recovery.
PST files are a backup, compliance, and support headache. A small change can cause a large file to be backed up again, and nobody has reliable visibility into what is inside them. I would migrate anything that must be retained, apply retention rules based on contractual and project requirements, and explicitly exclude or prohibit new PST storage after the migration.
Agreed. A fixed mailbox quota by itself can just push people toward storing mail somewhere less visible, so the policy and migration need to happen together.
That can be useful when the organization wants an independent archive, but I would avoid introducing another system unless the Exchange archive or existing backup platform cannot meet the requirements.