Smtp 来自Mailgun的电子邮件被Gmail拒绝

我正在使用邮枪在我的应用程序中发送电子邮件验证。我注意到发送到gmail地址的电子邮件总是被拒绝，而发送到其他地址（如yahoo mail）则没有问题。 以下是错误日志：

    "delivery-status": {
        "tls": true,
        "mx-host": "gmail-smtp-in.l.google.com",
        "attempt-no": 1,
        "description": "",
        "session-seconds": 0.44887804985046387,
        "utf8": true,
        "code": 550,
        "message": "5.7.1 [209.61.151.231      14] Messages missing a valid address in From:\n5.7.1 header, or having no From: header, are not accepted. e10si1791456oth.257 - gsmtp",
        "certificate-verified": true
    },
    "recipient-domain": "gmail.com",
    "event": "failed",
    "campaigns": [],
    "reason": "generic",
    "user-variables": {},
    "flags": {
        "is-routed": false,
        "is-authenticated": true,
        "is-system-test": false,
        "is-test-mode": false
    },
    "log-level": "error",

我怎样才能解决这个问题