Recently I migrated emails to my server (cPanel with MailChannels) (around 12 June) and since then customer is having problem with specific email addresses (specifically in sending).
If he sends (using Outlook/Thunderbird/MailSpring and other clients) any email to specific email address from his office/home (different computer/mobiles devices) it bounce back. He also run multiple tests via mail-tester/sparkpost/dkimvalidator (and you name it) all fails and shows DKIM/SPF/DMARC has issue.
(When he tries to send via webmail (Roundcube/Horde) no issue and it works just fine)
When I do the same (as he did) from my end, everything passes and works like a charm (no bounceback, DKIM/SPF all are validated without single error).
I am unable to understand what causing the issue, would it be email client (thunderbird,outlook) somehow modifying email headers (If yes then he already ran with different devices and clients) ? Or is it something related to their ISP or local firewall settings? I can provide test email header if you need to look into.
Thanks everyone, any help or suggestion would be great.
⚆ ͜ʖ ͡⚆ Thanked by (1281): verjin