No subject warning, but there is a subject
Hi everyone, For some weeks our user are reporting that Outlook gives a notification for 'no subject' when they send a mail. That is strange, because there is a subject in the mail. In some way, Outlook doesn't sees this subject. To make it even more strange, the issue does not occurs al the time. After restarting Outlook, it is away for some time. I tried serveral things to solve it - disabling plugins and updating Outlook among other things - but nothing has helped. The problem only occurs in Outlook 365 classic, with OWA there are no problems. Have any of you also encountered this problem? Kind regards, Arjan
Exchange RBAC Challenge: Restricting Admin Level Access to Selected Mailboxes
Hi Exchange Brain Trust, I'm looking to implement a restriction for a specific group of admins (let's say Service Desk L1 team) so they do not have administrative access to executive EXO mailboxes (e.g., email address removed for privacy reasons, email address removed for privacy reasons), while retaining access to all other mailboxes. I've explored built-in RBAC configurations, Administrative Units, and role assignments in Exchange, but haven’t found a solution that meets this requirement. Any guidance or suggestions would be greatly appreciated. Thanks in advance!
Exchange Outbound Email Delivery Failures - DNS Resolution Issue (Error 450 4.4.312)
Hi, Microsoft Exchange Online/Office 365 servers are failing to deliver emails to our mail server due to DNS resolution failures. This issue started approximately one week ago with no configuration changes on our end. All other email being delivered without problems. Any help or suggestions gratefully received ?? Technical Details Error Code: 450 4.4.312 DNS query failed [Message=ErrorRetry] Key Finding: Microsoft's Exchange servers are failing to resolve our domains when attempting email delivery, returning 0.0.0.0 during DNS lookups. Affected Domains: iteracy.com smartfixuk.com telexsus.com Multiple other domains hosted on our server's IP 148.253.141.57 Sample Error from NDR (sent to Microsoft users): Server at iteracy.com (0.0.0.0) returned '450 4.4.312 DNS query failed [Message=ErrorRetry] [LastAttemptedServerName=iteracy.com]' Email Flow Issue Problem: Microsoft users sending emails to our domains (e.g., mailto:email address removed for privacy reasons → mailto:email address removed for privacy reasons) are getting delivery failures because Microsoft's outbound mail servers cannot resolve our domain's mail server. DNS Configuration (All Working Correctly) Domain: iteracy.com MX Record: mail.iteracy.com (priority 0) A Record: mail.iteracy.com → 148.253.141.57 PTR Record: 148.253.141.57 → server.iteracy.com Nameservers: ns1.iteracy.com, ns2.iteracy.com (both → 148.253.141.57) Extensive Testing Performed DNS Providers That Resolve Our Domains Correctly: ? Google DNS (8.8.8.8) ? Cloudflare (1.1.1.1) ? Multiple global DNS propagation checkers Microsoft Exchange Online Specific Issues: ? Microsoft's outbound mail servers return 0.0.0.0 when looking up our domains ? Seemingly only Microsoft's mail infrastructure affected ? Multiple domains on same server IP affected ? Email delivery from any Microsoft system (Office 365, Outlook.com) to our domains fails What We've Ruled Out IP Blacklisting: Checked Microsoft's delisting portal (sender.office.com) - IP not blocked DNS Configuration: All records correct and resolving globally on all other DNS providers Recent Changes: No DNS, hosting, or configuration changes made Reverse DNS: PTR records properly configured and resolving correctly Business Impact Complete email isolation from Microsoft ecosystem (Office 365, Outlook.com, Hotmail, etc.) Microsoft users cannot send emails to our domains Client complaints and business disruption Messages temporarily queued but will eventually bounce if not resolved Support Experience Microsoft front-line support claims "not our issue" despite evidence that only Microsoft's outbound mail servers are failing DNS resolution for our domains.Managing Large Shared Mailboxes in Exchange Online – Performance Strategies and Trade-offs
Hey everyone, We’re managing very large shared mailboxes (>30 GB) in Exchange Online. These mailboxes are accessed by multiple users, with constant activity — dozens of emails being read, moved, flagged or replied to per minute. Now: - If we cache the shared mailbox in Outlook, the .ost file grows massively (10–20+ GB), which leads to local performance issues and even sync glitches. - If we don’t cache, then Outlook has to fetch everything live from Exchange Online, which introduces delays and makes search slower or inconsistent. => So basically, performance sucks either way. What we’ve learned so far: Shared mailboxes are treated like secondary mailboxes in Outlook, meaning: They sync slower than the primary mailbox. Push notifications from Exchange are limited or absent. Outlook often polls instead of getting real-time updates. Microsoft applies throttling policies per mailbox and tenant, which affects shared mailboxes with many concurrent users. OWA (Outlook Web Access), and the new Outlook app (One Outlook), use a persistent connection (WebSockets / streaming), allowing true real-time updates — no polling, no .ost reliance, no lag. The classic Outlook (Win32) client relies on MAPI and old-style caching behavior, which makes it less ideal for fast-paced shared mailbox environments. What we’re now considering: Should we move high-activity shared mailboxes to be accessed via OWA or the new Outlook app, where real-time sync is better? Should we split large shared mailboxes into smaller functional ones (e.g. support@, sales@, escalations@) to reduce contention? Should we still use caching, but limit it to Inbox + Sent Items and 3–6 months, and invest in better client hardware (faster SSDs, 16–32GB RAM)? Is it worth mapping shared mailboxes as full secondary accounts rather than traditional shared folders, to improve sync reliability (with the right licensing)? Or should we just give users personal mailboxes instead, and use distribution groups or automation for collaboration?
