Do this before you promise anything
The gap between signing a client and understanding their infrastructure is usually several weeks, and it is exactly the period in which something can lapse and become your fault.
One: establish what actually exists
Run a check on the domain. It reports the registrar, the renewal date, the certificate and its expiry, the mail setup and whether it passes, the hosting, and every subdomain still resolving. That takes seconds and gives you an inventory rather than an assumption.
The subdomains are the interesting part. Expect to find at least one thing nobody mentioned.
Two: find out who actually holds it
- Is the domain on an account the client controls, or on a former designer's personal account
- Is the registrant contact a person who still works there
- Is the payment card on file current
- Is transfer lock on
- Who has access to DNS, which is often a different provider from the registrar
If the answer to the first question is unclear, that is the most urgent item on this list and it is more urgent than anything on the website. Recovering a domain from a former supplier takes weeks, and it is far easier while the relationship is merely ended rather than acrimonious.
Three: check the things with dates on them
Domain renewal, certificate expiry, and any hosting or mailbox subscription. Anything inside ninety days is a live risk you have just inherited.
Four: check mail actually works
Not whether it sends. Whether it passes authentication for external recipients. A client whose invoices have been going to spam for a year without anyone realising will attribute the improvement to you when it is fixed, which is a reasonable way to start a relationship.
Five: write it down somewhere that outlives you
The inventory you just built is the handover document that did not exist before you arrived. Whether you keep it in a record, a wiki or a document matters less than that it exists and is dated, because the same problem you just solved for this client is the one your successor will face.
The commercial note
Several agencies bill this first-week audit as a discrete piece of work, and it is genuinely worth paying for, because it converts an unknown liability into a written list. It also surfaces the domain ownership problem at the only point where fixing it is easy.