WITH major_servers AS (
    SELECT email_server
    FROM email_address
    GROUP by email_server
    HAVING count(*) >=6
),
enumerated_emails AS (
    SELECT email,
           email_server,
           row_number() OVER (PARTITION BY email_server ORDER BY email) AS row_number --TODO:: ORDER BY email - attention
    FROM email_address
    WHERE email_server IN (SELECT email_server FROM major_servers)
)
UPDATE email_address
SET valid = true
WHERE email IN (SELECT email
                FROM enumerated_emails ee
                WHERE ee.row_number <= 3);

• 第一个查询major_servers查找存在5个以上电子邮件服务器的主要组。
• 第二个查询enumerated_emails使用窗口函数row_number()按照邮件的自然顺序（* 请参见TODO注解，我认为您应该选择另一个ORDER BY条件 *）枚举属于主要组的邮件。
• 最后一个查询更新每个主要服务器组中的前3行。

在此处查找sql-fiddle。

你需要获得服务器，然后排序邮件从哪个，然后执行更新。

WITH DataSourceServers AS 
(
    SELECT "EmailServer"
    FROM public."EmailContacts"
    GROUP by "EmailServer"
    HAVING count(*) >=6
),DataSourceEmails AS
(
    SELECT "Email", row_number() OVER (PARTITION BY "EmailServer" ORDER BY "Email") AS rn
    FROM public."EmailContacts"
    WHERE "EmailServer" IN (SELECT "EmailServer" FROM DataSourceServers)
)
UPDATE public."EmailContacts"
SET "Valid" = true
FROM  public."EmailContacts" E
INNER JOIN DataSourceEmails SE
WHERE E."EmailServer" = SE."EmailServer"
    AND E."Email" = SE."Email"
    AND SE.rn <= 3;