There are several reasons for this problem happen, like TLS, network, etc.
But this is a tip for emergence. If you for example try telnet email_server email_smtp_port (25,465 or 587 in general) on local network and Exim has an quickly response, but when you try the same command on external network and got a delay of 20 to 40 seconds to get initial server mail answer, please check your configuration an set dc_minimaldns to ‘true’
On Debian using spitted Exim4 configuration files, it can be done on /etc/exim4/update-exim4.conf.conf.
Just add or change the option to dc_minimaldns=’true’
Do not forget to reload Exim4 configuration and regenerate any configuration file if required. If this change solve the problem, now you can hold your email server working while now you have time to understand the real reason of the problem and solve it, restore your initial configuration.
Artigos relacionados:
SMTP protocol synchronization error (input sent without waiting for greeting): rejected connection from H=localhost [127.0.0.1] input=”\026\003\001\002″
Exim4 demorando a responder conexão SMTP externamente
Python – Enviando email utilizando o Gmail
Exim – Forçar execução da fila de entrega com tentativa de limpar as mensagens congeladas
Estrutura base do arquivo de configuracao do Exim4
Exim4 – Tamanho máximo de um anexo
Angular 4 – Corrigindo o problema de Response.headers.get(‘Content-Disposition’) sempre com valor null
Obtendo a fila de envio de mensagens do Exim4
Remover mensagens da fila de envio do Exim4