Robbogeordie

It could well be that making a bunch of changes has reset the "trust" level to 0, and all you can do is wait it out. In the meantime, you may have to remind users during signup and order processing to "whitelist" your domain, or to at least check their junk/bulk/spam mail folder.
Also keep this thread in mind:
 

You really should make your best attempt at changing the code per my post above.
It should still be very close to your files, maybe just different line numbers.

@Robbogeordie

I have tested my outlook inbox and no troubles but there are no way to see email headers in outlook.com so I reply to this email and I can see email header in thunderbird.
You can receive order emails directly into thunderbird with pop3 or imap protocol. (I didnt)

What do you see in junked email header?

I see this is no spam for me
X-MS-Has-Attach: yes X-MS-TNEF-Correlator: x-incomingtopheadermarker: OriginalChecksum:2BF954F7F7BC7201495F74ABE3C788684747FB4907CB283F6568D73F6055E7F6;UpperCasedChecksum:E83479C22438CCE30610154D42C222F1370F4471C54AF81D7B41F96CCF5FD496;SizeAsReceived:7031;Count:46 x-ms-exchange-messagesentrepresentingtype: 1 x-tmn: [rxUBREUSGI/f57cUW1bLGPfjQ+dYWA88] x-ms-publictraffictype: Email x-microsoft-exchange-diagnostics: 1;HE1EUR01HT099;6:7XfHZRWPVrAsK4waiCsfIj6ZFKyb5iwUVdBju+hnXF6XzDa/WcD+6096NUD32tWXETPWjHO4JJrGccyRGLjGgoIWzxiVnNsVB6eWgTwxNFmxMCQPOwthEuGVAgEh0Twk6UUh4fZWuGfPZTMa//4XvMLIvQjNWoEZOOKZMbZlXFTxDqfuT39/UF9W7pA/l3rCQkgDcbaI2DeMh9chFMA/UnX+bLFRPpeghBfP0GVXW24PdcFsdc5uRIhrsgSe+FtLr0+HFFH8JwOaJLY18DYic9Zp3F65pCuPcMqqpR+8judO1aKsM1hNIbLR/DlRalFRS4suqjFDyVIbPr3MjShUgJJHDJKFBh5sJC9Ifb/ytjU=;5:AVEgDFJ8sSO7W9zZtnI/vT60yTiallgLywDEu4n1ySfrU2UfBLuI0kgBdRP3rR53kN4Jlq3CM3bZus54ohJdmZIKixv9S/1ZFBgKXLYz81C3NSk5ljuV3XVJotgc8k0S2YuNQ8bgq7RzXiEljO/JxDrfwxp/CiQIg6WYs3RB9lU=;24:gUquGFIc8Kyrtp8w5qrmeJGfXO7lFEPGiT6YNKKkJW3k0VKCp1JxODuHj3vTCSclqM1VJOw9GoN0QhVZHEmV1xNPvkIuGf6921Bm1rrJfTo=;7:a/BVv08v7ZjeYeu0SWBWX5JCtVr7vQJqc6aBlvyR8zgk8f4ns5dAlictldhW7m5Y6N8mNtQUhIcR9ilNJHarQ3xI+apw6CS6t20MH7CSdtX7rJDseJN4vLzmAmrO2KlSsOXznJeDmzWQtKc1X4NA4tjnhCuqet+OWaJSk+Dxn9TWGBNLwtORiSZNvCwo++ivCE2VxK+IZ0r7NUdSP4BHGOC4k/CRGQXhTVMx4Xu/d+gh5qytJCdK6/JXeUjSESA1 x-incomingheadercount: 46 x-eopattributedmessage: 0 x-microsoft-antispam: UriScan:;BCL:0;PCL:0;RULEID:(7020095)(201702061074)(5061506573)(5061507331)(1603103135)(2017031320274)(2017031324274)(2017031323274)(2017031322404)(1603101448)(1601125374)(1701031045);SRVR:HE1EUR01HT099; x-ms-traffictypediagnostic: HE1EUR01HT099: x-ms-office365-filtering-correlation-id: c2c1873b-a9af-45e6-ab2d-08d5749b97c6 x-exchange-antispam-report-cfa-test: BCL:0;PCL:0;RULEID:(444000031);SRVR:HE1EUR01HT099;BCL:0;PCL:0;RULEID:;SRVR:HE1EUR01HT099; x-forefront-prvs: 058441C12A x-forefront-antispam-report: SFV:NSPM;SFS:(7070007)(98901004);DIR:OUT;SFP:1901;SCL:1;SRVR:HE1EUR01HT099;H:DB6P192MB0232.EURP192.PROD.OUTLOOK.COM;FPR:;SPF:None;LANG:; spamdiagnosticoutput: 1:99 spamdiagnosticmetadata: NSPM Maybe the x-forefront-antispam-report shows the trouble.