SMTPSenderRefused: (501, '5.1.7 Invalid address', 'ElastAlert') · Issue #1790 · Yelp/elastalert · GitHub
501 Bad sender address syntax response from SMTP server when setting addresses · Issue #212 · maildev/maildev · GitHub
SMTP Error: 501 5.1.3 Bad recipient address syntax on empty Config.adminEmail · Issue #230 · dereuromark/cakephp-tools · GitHub
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SMTP Protocol Error: 501 5.1.7 Bad sender address syntax when sending mail from our printer through Nethserver - Support - NethServer Community
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