ROS based email relay?

RouterOS General
1

ROS itself does have an email client already. Can it be used for something trickier than configuration sending?
Namely I have 2 outside lines and in case of failure I have script controllable failover for Internet traffic, but I am unable to control outbound email server selections for internal computers. What is my options for automatic failover for outbound email sending?

2

Maybe destination NAT would work? As part of your existing fail over scripts enable and disable NAT rules that rewrite packet headers to direct mail traffic to specific servers.

3

If I have understood right, you may use static short-time DNS record of your mail server that will be rewriting using netwatch. So if line is up, smtp.my.com will be IP_1, else it will be IP_2.

If your clients are not using your DNS or are not using domain name of SMTP server, this will not work, of course - then you should use redirection in firewall controlled by netwatch.

4

Thanks, I’ll try out some of those proposed ideas.

5

I implemented that DNS based e-mail server changing system by setting 2 static DNS records with the same name to point to different ISP e-mail servers:

/ip dns
set allow-remote-requests=yes cache-max-ttl=1w cache-size=2048KiB \
    max-udp-packet-size=512 servers=a.a.a.a,b.b.b.b
/ip dns static
add address=x.x.x.x disabled=no name=mail.myownmail.yy ttl=5s
add address=y.y.y.y disabled=yes name=mail.myownmail.yy ttl=5s

And my other scripts detecting ISP link downing are invoking appopriate mail.myownmail.yy DNS record setting:

/system script
add name=email_one policy=\
    ftp,reboot,read,write,policy,test,winbox,password,sniff,sensitive,api \
    source=":local Items;\r\
    \n:local Item;\r\
    \n:log info message=\"Outbound e-mail set to y.y.y.y.\";\r\
    \n:set Items [/ip dns static find address=\"x.x.x.x\"];\r\
    \n:foreach Item in=\$Items do={/ip dns static disable \$Item};\r\
    \n:set Items [/ip dns static find address=\"y.y.y.y\"];\r\
    \n:foreach Item in=\$Items do={/ip dns static enable \$Item};"
add name=email_two policy=\
    ftp,reboot,read,write,policy,test,winbox,password,sniff,sensitive,api \
    source=":local Items;\r\
    \n:local Item;\r\
    \n:log info message=\"Outbound e-mail set to x.x.x.x.\";\r\
    \n:set Items [/ip dns static find address=\"x.x.x.x\"];\r\
    \n:foreach Item in=\$Items do={/ip dns static enable \$Item};\r\
    \n:set Items [/ip dns static find address=\"y.y.y.y\"];\r\
    \n:foreach Item in=\$Items do={/ip dns static disable \$Item};"

Note: a.a.a.a, b.b.b.b, x.x.x.x, and y.y.y.y are site specific.