Sender Policy Framework and ISP's blocking port 25 seems problematic
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Can I change outgoing port 25 to port 587 or any other port · Issue #1134 · postalserver/postal · GitHub
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Which SMTP Port to Use for Email: 25, 587, 465, or 2525?
ISP blocks SMTP port 25 - Bypass/Fix - ALI TAJRAN
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Testing Port 25
All About Port 25, 465, 587, 143, 993, 110 and 995 -
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Which SMTP Port to Use for Email: 25, 587, 465, or 2525?
Bypassing Hetzner mail port block (port 25/465) - Jan van den Berg
Which SMTP Port Should I Use? Understanding Ports 25, 465, & 587 | Mailgun
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Cannot send SMTP mail on port 25, try port 587 - Niall Best's Blog
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What is Port 25?
Switching from SMTP port 25 to port 587 – HELP CENTER
Which SMTP Port to Use for Email: 25, 587, 465, or 2525?
SMTP Port 25, 465, 587, 2525: Which Port Should I Use?
Which SMTP Port to Use for Email: 25, 587, 465, or 2525?
