###### tags: `Ubuntu`,`Mail Relay`, `Pstfix`
# Ubuntu 20.04 + Postfix 做Mail Relay

1. 更新

sudo apt update

2. 安裝Postfix 套件

sudo apt install postfix

3. 選擇 <font color=#FF6600>Internet Site </font>模式

4. 輸入主機名稱 EX: <font color=#FF6600>mailrealy.example.com</font>

### 重點來啦!!
5. 配置主機參數

編輯 /etc/postfix/main.cf，輸入：

sudo nano /etc/postfix/main.cf

main.cf內容:

# See /usr/share/postfix/main.cf.dist for a commented, more complete version


# Debian specific:  Specifying a file name will cause the first
# line of that file to be used as the name.  The Debian default
# is /etc/mailname.
#myorigin = /etc/mailname

smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no

# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h

readme_directory = no

# See http://www.postfix.org/COMPATIBILITY_README.html -- default to 2 on
# fresh installs.
compatibility_level = 2

#25            inet      n      -       n       -       -        smtpd

# TLS parameters
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_tls_security_level=may

smtp_tls_CApath=/etc/ssl/certs
smtp_tls_security_level=may
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache


smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
myhostname = mailrelay.example.com  //mailrelay 主機名稱
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = /etc/mailname
#myorigin = $myhostname
mydestination = localhost.$mydomain, localhost, $myhostname
#mydestination=
relayhost = [smtp.office365.com]:587 //此為O365 SMTP伺服器
mynetworks =  127.0.0.0/8 192.168.0.0/24 //輸入區網IP 用空白分隔
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all
#inet_protocols = all
inet_protocols = ipv4

smtp_sasl_auth_enable = yes
#smtp_sasl_password_maps = static:[e-mail]:Password 
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous
smtp_tls_security_level = may
#header_size_limit = 4096000

#### 需要注意的是 :
myhostname : Relay主機名稱
relayhost : 此用O365做SMTP伺服器，若是其他主機就設定該主機上的SMTP伺服器
mynetworks : 區網IP
inet_interfaces : 誰可以傳進這台主機
inet_protocols : 使用IPV4即可
smtp_sasl_password_maps : 這裡有兩種寫法, 一種是直接寫死(如53行),另一種是另外做一個檔案把相關參數放在該檔案裡(54行)

帶設定都完成後跳出並重啟Postfix服務:

 sudo systemctl restart postfix

#### sasl_passwd 內容:
剛剛說到把smtp_sasl_password_maps放在另一個檔案內所以需要在該檔案(檔案位置在/etc/postfix/)內新增下面內容
[smtp伺服器]:port號 帳號:密碼

[smtp.office365.com]:587 [e-mail]:Password  

當Postfix都設定完成後記得要開啟防火牆 Port 25

sudo ufw allow 25/tcp
sudo ufw restart //重開防火牆

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#### 當都完成後就可以來測試了
1. 首先確認是否有把該主機加入DNS內,因一不小心就可能被當跳板亂發信所以建議設定在內部使用就好。
2. 再來要檢查port 25是否正常開啟運作
指令:

sudo netsta -tuln


telent 測試,開啟命令提示字元
指令:

telnet 192.168.XXX.XXX 25

若成功就下面文字代表已經TELNET進去POSTFIX服務裡

安裝 Mailutils 套件

sudo apt install mailutils

安裝後可測試發信看看,若收到信就代表成功了
指令:

 echo "This is a test email body." | mail -s "Subject title" -a "From: [e-mail]" [e-mail]

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### 參考網站:
-[連結一](https://apiit.atlassian.net/wiki/spaces/ITSM/pages/1205567492/How+to+configure+postfix+relay+to+Office365+on+Ubuntu)
-[連結二](https://magiclen.org/ubuntu-server-email/)