title: Emails sent with MimeKit / Outlook are falling to gmail's spam folder for the first time
body: <p>We are using MimeKit as SMTP client for sending emails to our users. Typically, the first time it arrives to their gmail accounts, it falls into the spam box. Then if removed the 'spam' flag, subsequent emails stay in the inbox.</p>
  
  <p>Is there something necessary to do at C# level? or maybe at Outlook/Azure-DNS level?</p>
  
  <p>The C# code snippet is as follows:</p>
  
  <pre class="lang-cs prettyprint-override"><code>            var message = new MimeMessage();
              message.From.Add(new MailboxAddress("Notifier", smtpUser));
              message.To.Add(new MailboxAddress("User", recipient));
              message.Subject = subject;
  
              var bodyBuilder = new BodyBuilder() { HtmlBody = html, TextBody = text };
              message.Body = bodyBuilder.ToMessageBody();
  
                  using (var client = new SmtpClient())
                  {
                      client.ServerCertificateValidationCallback = (s, c, h, e) =&gt; true;
                      client.Connect(current.SmtpUrl, current.SmtpPort, SecureSocketOptions.StartTls);
                      client.AuthenticationMechanisms.Remove("XOAUTH2");
                      client.Authenticate(current.SmtpUser, current.SmtpPass);
                      client.Send(message);
                      client.Disconnect(true);
                  }   
  </code></pre>
  
  <p>For the first time, gmail is showing it flagged as 'spam':
  <a href="https://i.stack.imgur.com/eX2j5.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/eX2j5.png" alt="enter image description here"></a></p>
  
  <p>Pressing 'Looks safe' will make subsequent emails valid, but we need the first one to look safe.</p>
  
  <p>I am attaching also the entire mail content received at gmail:</p>
  
  <pre><code>Delivered-To: jaimeolivaresfalcon@gmail.com
  Received: by 2002:a0c:f08c:0:0:0:0:0 with SMTP id g12csp672696qvk;
          Wed, 4 Sep 2019 07:16:38 -0700 (PDT)
  X-Received: by 2002:a9d:3b77:: with SMTP id z110mr8444689otb.93.1567606358405;
          Wed, 04 Sep 2019 07:12:38 -0700 (PDT)
  X-Google-Smtp-Source: APXvYqw3m+1ZsX0fhLp8SuYRXSxfxUtUaYyLo4BZjxq+nVuni9VUHkVmOBnhBg/vThsIaIoA3chE
  X-Received: by 2002:a9d:3b77:: with SMTP id z110mr8444615otb.93.1567606357487;
          Wed, 04 Sep 2019 07:12:37 -0700 (PDT)
  ARC-Seal: i=2; a=rsa-sha256; t=1567606357; cv=pass;
          d=google.com; s=arc-20160816;
          b=MvKIcQqivTBGk3GqNz9MiIMtzUt4gJc0hJMoVHp7LMJyHO+AAiPfDGAdQYy7MwF0YF
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           aOkw==
  ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816;
          h=mime-version:content-language:accept-language:message-id:date
           :thread-index:thread-topic:subject:to:from:dkim-signature;
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           1Xvw==
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         arc=pass (i=1 spf=pass spfdomain=efferenthealth.com dkim=pass dkdomain=efferenthealth.com dmarc=pass fromdomain=efferenthealth.com);
         spf=pass (google.com: domain of notifier@efferenthealth.com designates 2a01:111:f400:fe44::629 as permitted sender) smtp.mailfrom=notifier@efferenthealth.com
  Return-Path: &lt;notifier@efferenthealth.com&gt;
  Received: from NAM02-SN1-obe.outbound.protection.outlook.com (mail-sn1nam02on0629.outbound.protection.outlook.com. [2a01:111:f400:fe44::629])
          by mx.google.com with ESMTPS id k12si10006003oiw.30.2019.09.04.07.12.37
          for &lt;jaimeolivaresfalcon@gmail.com&gt;
          (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128);
          Wed, 04 Sep 2019 07:12:37 -0700 (PDT)
  Received-SPF: pass (google.com: domain of notifier@efferenthealth.com designates 2a01:111:f400:fe44::629 as permitted sender) client-ip=2a01:111:f400:fe44::629;
  Authentication-Results: mx.google.com;
         dkim=pass header.i=@efferenthealthllc.onmicrosoft.com header.s=selector2-efferenthealthllc-onmicrosoft-com header.b=ETAIKEtN;
         arc=pass (i=1 spf=pass spfdomain=efferenthealth.com dkim=pass dkdomain=efferenthealth.com dmarc=pass fromdomain=efferenthealth.com);
         spf=pass (google.com: domain of notifier@efferenthealth.com designates 2a01:111:f400:fe44::629 as permitted sender) smtp.mailfrom=notifier@efferenthealth.com
  ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=NNjokEVhuXR5/dOYj6NjeePpEmQbWt5XFctGf5IRGJuGMHAuAd9cXjCTkqduSGP3bTLRqIYjwDRthcj10zcZVudxgjhe6OB50s8KJAMpXVdh+HvGD1JoqUq2BW9M0qyOQ0YDl6Fq6F3DAWMpWNIZRPlrlaOkNaO8ifHj1okiSrThxzIxuGkzGx5iUt8/S7LOBuvzgkVWoT0NendRzvl/mB1ZQgYWcpBa+PulPlYgCTtktO1rbYZgKr5qFvJGbgBvQ1bnyZtHmZRQrA7mNegfeXrK544dGEcXs1DcFo+vNeNR53dvBWFyPCkmPpdl4+rKGRkfo/PY3B1M+D003HXuqQ==
  ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=LjkQ2fZg1ziyuIJx9jwPMT7LT3T4ABbJmFUMJxavtNY=; b=G0nSGcuGCOFD8gcKNWVcBAZ2EIGwicBs0yITe0iyVc+3BIm2/QUfSzcPk0+FRIKtklfUru/c/sTaag3j/6RwPp98uj+2I8k/hdLY0+72qvx595t+E+CMXSGyLmBxHYEcgIzWuckwnRdnUaeU0LwLsqKiCLV1QakRniWXnlzdKjvAXozRlHfnx/AOmyGGYUc5u1zTM5VJWmxprCL+bqEOZi1agY4A94MJK5UyW+YEOEgNEJuyx1+pgdpeQkYVqeYVAk5AcFKLgYNBLpxvW0oVqRMECOV6zlI8xJU8qiFaW64qrBQVYQF8nRfQZd8oI3nmIIoPrstNWqgEOH/UEajoNA==
  ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=efferenthealth.com; dmarc=pass action=none header.from=efferenthealth.com; dkim=pass header.d=efferenthealth.com; arc=none
  DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efferenthealthllc.onmicrosoft.com; s=selector2-efferenthealthllc-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=LjkQ2fZg1ziyuIJx9jwPMT7LT3T4ABbJmFUMJxavtNY=; b=ETAIKEtNCHLfnl7Fzp8XUI+NlLP/HVTzkmlFS6XwZsLZP5vOj0hJ+1KASa6mjEAvPJbmM2iDTvCMRW8UfigfVSC6hT04OyaiGjNzOjTkR8gN1TCvzNr7esQzyXR94vmz2MjLiycuhNJJMdGGRUoYZUxGhvj6F0muEBoZZ034GLQ=
  Received: from BN6PR1401MB2004.namprd14.prod.outlook.com (10.174.116.149) by BN6PR1401MB1907.namprd14.prod.outlook.com (10.174.115.146) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.2220.18; Wed, 4 Sep 2019 14:12:35 +0000
  Received: from BN6PR1401MB2004.namprd14.prod.outlook.com ([fe80::1de9:93da:5da7:4415]) by BN6PR1401MB2004.namprd14.prod.outlook.com ([fe80::1de9:93da:5da7:4415%11]) with mapi id 15.20.2220.022; Wed, 4 Sep 2019 14:12:35 +0000
  From: Notifier &lt;notifier@efferenthealth.com&gt;
  To: User &lt;jaimeolivaresfalcon@gmail.com&gt;
  Subject: Notification
  Thread-Topic: Notification
  Thread-Index: AQHVYyrMLhjkfFeVAkmoUM8Y198VPw==
  Date: Wed, 4 Sep 2019 14:12:34 +0000
  Message-ID: &lt;98UUW7B0H8U4.EB3P8CQCSUEN2@localhost.localdomain&gt;
  Accept-Language: en-US
  Content-Language: en-US
  X-MS-Has-Attach: 
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  authentication-results: spf=none (sender IP is ) smtp.mailfrom=notifier@efferenthealth.com;
  x-ms-exchange-messagesentrepresentingtype: 1
  x-originating-ip: [13.84.163.72]
  x-ms-publictraffictype: Email
  x-ms-office365-filtering-correlation-id: 6291f624-e9b1-484f-f114-08d73141eea5
  x-microsoft-antispam: BCL:0;PCL:0;RULEID:(2390118)(7020095)(4652040)(7021145)(8989299)(4534185)(7022145)(4603075)(4627221)(201702281549075)(8990200)(7048125)(7024125)(7027125)(7023125)(5600166)(711020)(4605104)(1401327)(2017052603328)(7193020);SRVR:BN6PR1401MB1907;
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