Introduction

A mail migration can move the mailbox successfully while phones and tablets still try to sync against the old server through ActiveSync. Desktop Outlook may already work, webmail may already be correct, and the user may appear fully migrated, but mobile devices keep following an older server profile or stale autodiscover path.

Treat this as a device-profile and discovery problem instead of a general mailbox outage. Start by checking what server name the mobile device is actually trying to reach, because ActiveSync failures often survive a migration when the account profile was never rebuilt for the new platform.

Symptoms

  • Mobile devices still connect to the old mail server after migration
  • ActiveSync keeps prompting for credentials even though the mailbox password is correct
  • Outlook mobile, iPhone Mail, or Android mail apps fail while webmail still works
  • Some devices work after migration, but older enrolled devices still point to legacy infrastructure
  • Account reauthentication sends users to the previous server name
  • The issue started after mailbox migration, provider change, or Exchange cutover

Common Causes

  • The mobile mail profile still stores the old ActiveSync server name
  • Autodiscover still returns legacy mobile settings for some users or domains
  • MDM or configuration profiles keep reapplying the previous Exchange server
  • The device account was migrated, but the existing mobile profile was never recreated
  • Cached credentials and stale account metadata hide the real server mismatch
  • One domain or alias still publishes an old discovery path used by mobile clients

Step-by-Step Fix

  1. Check the exact server name, domain, or discovery path the affected mobile device is trying to use, because you need to prove whether the failure is tied to a stale ActiveSync target.
  2. Confirm the mailbox works through webmail or another known-good client, because that separates mobile profile failure from a wider mail outage.
  3. Review autodiscover and related mail-discovery records for the affected domain, because mobile clients often keep following a published path that was not cleaned up after migration.
  4. Check whether an MDM platform, mobile configuration profile, or corporate enrollment policy is pushing the old Exchange server back onto the device, because manual fixes do not stick if device management keeps restoring legacy settings.
  5. Remove and recreate the affected mobile account only after confirming the intended new server or provider settings, because repeated password resets do not fix a profile still targeting the wrong host.
  6. Compare one newly configured device with one failing older device, because differences in profile age or enrollment method usually reveal why only some phones remain on the legacy path.
  7. Test with the exact domain, alias, and username format the mobile client expects, because ActiveSync profiles often fail only on one login identifier after a migration.
  8. Verify the old server is no longer answering mobile sync requests in its logs, because successful mailbox access elsewhere does not prove ActiveSync traffic has left the legacy environment.
  9. Document the final mobile setup method and any MDM dependencies after recovery, because ActiveSync issues often return during later mailbox migrations when old device profiles are left in place.