Say what is affected first
Open with the thing customers care about: which feature is down and who is affected. Leave the technical cause for later, or for the write-up after the incident.
Investigating: admit what you know
A good first update is two sentences. We are investigating problems with sign-in. Some customers may see errors. We will post another update within 30 minutes. Promise a next update time and keep it.
Identified: name the cause in plain words
Once you know the cause, say so without jargon. We found a problem with our email provider and are working on a fix. Add what customers can do meanwhile, if anything.
Resolved: confirm and apologise once
Say the service is working again, give the time range and apologise in one sentence. Tell people what to do if they still see a problem, and link a contact route.
Keep the tone steady
Avoid blame, hype and promises you cannot keep. Short and calm updates build more trust than long ones. Use the same wording in your saved replies so email and status page agree.
Update on a schedule
Silence reads as trouble. Post at the cadence you promised even when there is nothing new, and write it as no change, still working on it. Then link the page in your auto-reply.