Correct SPF record to avoid softfail for emails sent from domain address using Gmail?

I have a domain address, such as [email protected], which forwards to Gmail. Gmail is configured to 'send email as' [email protected], using example.com's SMTP server.

Emails sent from Gmail as [email protected] to another Gmail address deliver fine. Replies to that email back to [email protected], are going into spam.

Every one of those replies comes in with the following message in the header:

spf=softfail (google.com: domain of transitioning [email protected] does not designate IP_ADDRESS_OF_EXAMPLE.COM_MX as permitted sender) [email protected];

I have adjusted the spf DNS record for example.com to contain: v=spf1 mx include:netblocks.dreamhost.com include:relay.mailchannels.net include:_spf.google.com -all

(The first two are what Dreamhost, my domain host, default to. I added google.com).

I had thought that adjustment would fix it, but I'm clearly missing something. What is it?

UPDATE -- full header pasted below. I've replaced email addresses with PERSON1 (the Gmail account configured to send as [email protected]), PERSON99 (the gmail account being sent to and replied from), and [email protected] as above:

Delivered-To: [email protected]
Received: by 2002:a0c:ffce:0:0:0:0:0 with SMTP id h14csp219058qvv;
        Wed, 24 Mar 2021 02:57:38 -0700 (PDT)
X-Google-Smtp-Source: ABdhPJwBCKVNM176Kci8wKH2Ok8kvwMvoTHZwIyDHC85JoNXx0qqfleGv7BkrehLNC7//RVelwcc
X-Received: by 2002:a17:90b:3716:: with SMTP id mg22mr2579388pjb.157.1616579858373;
        Wed, 24 Mar 2021 02:57:38 -0700 (PDT)
ARC-Seal: i=1; a=rsa-sha256; t=1616579858; cv=none;
        d=google.com; s=arc-20160816;
        b=nWxwOQwSSO4CG4muH1Ts9tHF8Wi30YpaPHFLXux8ysocZePKwzCp6DlLdo/h3RlTnT
         oFcVykFbuMLWzJyqNBdlHeXUJwnl5vg0TRnSDH1dM9Hn9q4VwVgkh01kTtciYfHpi8TM
         D12M2rkfCRNSpJB5tBuLz8FIyXcz4453vjsxrBhq0bJgSdrMInO+GsCCYyCzkAq8agHL
         0ZdM6LhoM5Y5NvuxCeoPZSFRZdkXlhVubiU7/Ou/G5o0+ktEo0e3otwwPCcuufEGpUzw
         3CNMiock7VlySx85tyAVlKE1exk49R55Me1+XILaemeiMiiaiidoTcCQ1ypjfhlVDp1S
         TC8w==
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816;
        h=to:subject:message-id:date:from:in-reply-to:references:mime-version
         :dkim-signature;
        bh=IxbTYU9ihz312Yq0VFwswippxC7wgB0q/P4K8ivRjh8=;
        b=jzf3qfhCi4ggMh/m0ZAoYVmMfIHYZdfEvGxQrG5K70VJ5mch9smO01kp5zg0hnmQ2R
         vZdS6pGtD7V4R62+k12SDJ8teZboqjqCtUQpFczUZhbI9rpFcgqtCs3cn72odaGPAN6P
         L10ydmf9DABbEwqCm4B+15S8/0fZMwyuPWDEQcTB/nNj/ff0yuQ87zdviBw9fhFI2NCY
         mC+7+x2DlZJt8t2hZmAGLyZne0RKVQ4WWKCCIeIhyz0oXri+bu8DRC1Z/fIGNx9DVtM2
         BtLkDo8x01PrsBK54rpsoCx2ktXFU4hl67cgylfcvLKQDs/U7FBMziJOsfXCylHz1nai
         yWSA==
ARC-Authentication-Results: i=1; mx.google.com;
       dkim=pass [email protected] header.s=20161025 header.b=hNgluIwd;
       spf=softfail (google.com: domain of transitioning [email protected] does not designate 64.90.62.163 as permitted sender) [email protected];
       dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com
Return-Path: <[email protected]>
Received: from pdx1-sub0-mail-mx18.g.dreamhost.com (mx1.dreamhost.com. [64.90.62.163])
        by mx.google.com with ESMTPS id e25si1847211pgl.414.2021.03.24.02.57.38
        for <[email protected]>
        (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128);
        Wed, 24 Mar 2021 02:57:38 -0700 (PDT)
Received-SPF: softfail (google.com: domain of transitioning [email protected] does not designate 64.90.62.163 as permitted sender) client-ip=64.90.62.163;
Authentication-Results: mx.google.com;
       dkim=pass [email protected] header.s=20161025 header.b=hNgluIwd;
       spf=softfail (google.com: domain of transitioning [email protected] does not designate 64.90.62.163 as permitted sender) [email protected];
       dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com
Received: from mail-wm1-f53.google.com (mail-wm1-f53.google.com [209.85.128.53]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by pdx1-sub0-mail-mx18.g.dreamhost.com (Postfix) with ESMTPS id AD929AEB7B for <[email protected]>; Wed, 24 Mar 2021 02:57:37 -0700 (PDT)
Received: by mail-wm1-f53.google.com with SMTP id k128so10133768wmk.4
        for <[email protected]>; Wed, 24 Mar 2021 02:57:37 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
        d=gmail.com; s=20161025;
        h=mime-version:references:in-reply-to:from:date:message-id:subject:to;
        bh=IxbTYU9ihz312Yq0VFwswippxC7wgB0q/P4K8ivRjh8=;
        b=hNgluIwd0E0Zx/hvBSVbpKFr7VAZKIUpzTMqnDJ/rSeQOj1vWblPddfOYC1lVrh6ZB
         NGp4pw4gUQV4JUDSU5WKdyDYrE+cOzZgs4/63uNYxQljwLbwsxDq+BDUTKvpCFuYU/hy
         MHZsOCga8Rv8guxACVHKJZOgWni4xxnNxfdxNqOeIlhQQ1Tf7ZhzdkOusUd6Cr3BVl+4
         Ix2FiJ31KOYoy/6ElxswiVV1v+EWBFT+aVQO3Mifup1dBa2mQLLtlQmvFQG/QUlQMMcJ
         KzMfCQT8ao4zAf4sn9YREwLpwTLXpo/uHnF55xCfTAl398BrQ5gKnHTfWVF51vjWN9RQ
         0ltA==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
        d=1e100.net; s=20161025;
        h=x-gm-message-state:mime-version:references:in-reply-to:from:date
         :message-id:subject:to;
        bh=IxbTYU9ihz312Yq0VFwswippxC7wgB0q/P4K8ivRjh8=;
        b=I8NCHhqijKrpmBqE3/thZBtfSiyi67s1+GeTf2kQI62JQZbpT5MzSzGfsdwgDSNgvD
         TXA3nKuqv7dnpU35ZplnyDMghp/pUWcTsSE1znKZ7sX9jG6vTlIImHBvvNs6g9gzA3lV
         LgjLssA+pma0QuGQPZDsEDPx7+nxNL1EG7VDk6XCCicXet806EQxtq5UO2wiVp1ORnex
         iJpD63JDWjckDJ7LMM4bRso/oqNjArmKDBiAK22Ma/Z2zRVqf9Dv+hpkvMad7rFVdOQZ
         Mo6JNCe0l5L590VI7//8QU/I748rJodTcloe1Kt8p8TDFIX62OKMVnZj698ZCi15tsOf
         46Aw==
X-Gm-Message-State: AOAM530PRD38wY7l2GyuJJQJtnxvGBsjBGkAA3f0pHmo+mxqF52LHB2k 1+4iAH3cKmuoc72Q+/1ejOzbq5uxTxTOyLO/SSi8suUK
X-Received: by 2002:a05:600c:4f55:: with SMTP id m21mr2062135wmq.11.1616579855739; Wed, 24 Mar 2021 02:57:35 -0700 (PDT)
MIME-Version: 1.0
References: <CABnao97UwPfxpSTZvZYahxzFRn2aBQTmha1J4PP0LH2cHeb4Xg@mail.gmail.com>
In-Reply-To: <CABnao97UwPfxpSTZvZYahxzFRn2aBQTmha1J4PP0LH2cHeb4Xg@mail.gmail.com>
From: Julie Turner <[email protected]>
Date: Wed, 24 Mar 2021 04:57:24 -0500
Message-ID: <CAG7xKKru_OgpYSBgy5DxJ992jG=ddBqZkLo_F2DdpeQ+7-K-zg@mail.gmail.com>
Subject: Re: testing
To: ME <[email protected]>
Content-Type: multipart/alternative; boundary="0000000000000d6fc105be45545e"

Solution 1:

There is a problem with PERSON99 email settings. The mail from [email protected] is sent from dreamhost as shown in this header.

Return-Path: <[email protected]>
Received: from pdx1-sub0-mail-mx18.g.dreamhost.com (mx1.dreamhost.com. [64.90.62.163])
        by mx.google.com with ESMTPS id e25si1847211pgl.414.2021.03.24.02.57.38
        for <[email protected]>
        (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128);
        Wed, 24 Mar 2021 02:57:38 -0700 (PDT)

Only google may choose who is sending mail with addresses from @gmail.com -- that's the whole SPF point -- and 64.90.62.163 is not in google's list.