First, email communication is considered “in writing,” so there’s no particular concern that they are not communicating with via US Mail. The parties are bound by statements and commitments they make via email, and responding to Safeco via email is legally adequate. I assume the Safeco repair estimate was sent to you via email, probably from the adjuster assigned to your claim. If so you can and should communicate with Safeco regarding that estimate through that adjuster.
If s/he is willing to do so, ask your contractor to prepare an estimate which details the required work and materials, ideally using the Xactimate software Safeco used to create theirs. Most contractors are familiar with it, though some aren’t willing to put in the time required to create an Xactimate estimate, at least without getting paid to do it. If your contractor wants to be paid and you can afford it, I recommend paying the contactor to create a “rebuttal” Xactimate estimate because that will force the carrier to respond specifically to the significant differences between Safeco’s estimate costs and yours, and it will probably be worth the investment. If this isn’t possible, ask your contractor to create the most specific bid/estimate s/he is willing to prepare.
Send your alternate estimate to Safeco with a cover email that requests they respond to your estimate pursuant to Section 2695.9 of the California Fair Claims Settlement Practices Reguilations and quote the following provision:
If the claimant subsequently contends, based upon a written estimate which the claimant obtains, that necessary repairs will exceed the written estimate prepared by or for the insurer, the insurer shall:
(1) pay the difference between its written estimate and a higher estimate obtained by the claimant; or,
(2) if requested by the claimant, promptly provide the claimant with the name of at least one repair individual or entity that will make the repairs for the amount of the written estimate. The insurer shall cause the damaged property to be restored to no less than its condition prior to the loss and which will allow for repairs in a manner which meets accepted trade standards for good and workmanlike construction at no additional cost to the claimant other than as stated in the policy or as otherwise allowed by these regulations; or,
(3) reasonably adjust any written estimates prepared by the repair individual or entity of the insured’s choice and provide a copy of the adjusted estimate to the claimant.
Safeco’s response should provide a basis for you/your contractor to negotiate the differences.
As to the letter protecting your rights, send it to the adjuster from whom you have received the most recent communication, set the email to request “delivery” and “read” confirmations, and be sure it doesn’t get kicked back as undeliverable. If it does, call Safeco’s claim services phone number, have your claim number available, and ask who is currently assigned to your claim and get their email address and phone number.
I hope this is helpful and answers your questions.